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A diamond anvil cell with resistive heating for high pressure and high temperature x-ray diffraction and absorption studies
Abstract
In this paper we describe a prototype of a diamond anvil cell (DAC) for high pressure/high temperature studies. This DAC combines the use of a resistive oven of 250 W power in a very small volume, associated with special conical seats for Boehler-type diamond anvils in order to have a large angular acceptance. To protect the diamond anvils from burning and to avoid the oven oxidation, the heated DAC is enclosed in a vacuum chamber. The assemblage was used to study the melting curve of germanium at high pressure (up to 20 GPa) and high temperature (up to 1200 K) using x-ray diffraction and x-ray absorption spectroscopy.
... 3,4 In addition, note that the induction heating technique that heats the anvil seats with an induction coil is also abbreviated as IHDAC. 5 The previously reported EHDACs, except for the induction heating technique, 5 employed Joule heating from the heater placed in contact with 4,6 or in proximity to the diamond anvil and the gasket, [7][8][9][10][11][12][13][14][15][16][17][18] or surrounding the whole DAC body. 3,19 Various heater assemblies and shapes have been proposed for metallic [7][8][9][10][11][12][13][14] and semiconductor heaters, 4,6,15-18 reaching up to 1700 K for a metallic heater 13 and up to 1500 K for a semiconductor heater. ...
... 5 The previously reported EHDACs, except for the induction heating technique, 5 employed Joule heating from the heater placed in contact with 4,6 or in proximity to the diamond anvil and the gasket, [7][8][9][10][11][12][13][14][15][16][17][18] or surrounding the whole DAC body. 3,19 Various heater assemblies and shapes have been proposed for metallic [7][8][9][10][11][12][13][14] and semiconductor heaters, 4,6,15-18 reaching up to 1700 K for a metallic heater 13 and up to 1500 K for a semiconductor heater. 18 Physical property measurements using an EHDAC have become a growing challenge. ...
The externally heated diamond anvil cell (EHDAC) conducts high pressure and temperature experiments with spatial uniformity and temporal stability. These are conventionally combined with various spectroscopies and x-ray diffraction measurements. EHDAC techniques perform Joule heating on a heater placed close to or directly in contact with diamond anvils. However, the electrical wiring and heater required for Joule heating complicate EHDAC setups, hindering easy access for the measurement of physical properties. This study proposes an EHDAC technique using laser- instead of Joule-heating. We successfully achieved temperatures reaching 900 K by applying heat to diamond anvils through laser-heating of the gaskets with thermally insulating anvil seats. To test this setup, we measured the melting temperature of H 2 O ice VII, which was consistent with previous studies. We also measured the high-pressure and temperature impedance of H 2 O VII and verified the capability of electrical resistivity measurements in this setup. This technique allows various physical property measurements owing to its simple setup required for externally laser-heated diamond anvil cell experiments. The unique characteristics of this heating technique are that (1) no heaters or wiring are required, (2) it exhibits the most efficient heating among EHDAC studies, (3) it maintains the DAC body at room temperature, and (4) diamond anvils do not detach from anvil seats after the EHDAC experiment. This method significantly simplifies the experimental setup, which allows much easier access to various physical property measurements using an EHDAC.
... Therefore, researchers in this field aim to develop materials that can operate at higher temperature and high pressure. Synchrotron x-ray diffraction (XRD) coupled with resistor-heating or laser-heating diamond anvil cell (DAC) technique can provide microstructural information under high temperature and high pressure at the same time [22][23][24][25][26][27], which makes it possible to study performance of materials under both high temperature and high pressure. The high pressure can easily be generated through DAC by compressing small samples between two opposing diamond culets, while the high temperature can be generated by heating DAC through laser or resistor. ...
... Laser-heated DAC [23][24][25] has become an important tool, but the lack of temperature measurement accuracy is an ongoing problem [24]. On the other hand, an electrical heater with adjustable voltage and current out of the resistor heated DAC [27,28] makes it easier to precisely control and measure the temperature. ...
In this work, the performance of the carbon doped compositionally complex alloy (CCA) MoNbTaW was studied under ambient and high pressure and high temperature conditions. TaC and NbC carbides were formed when a large concentration of carbon was introduced while synthesizing the MoNbTaW alloy. Both FCC carbides and BCC CCA phases were detected in the sample compound at room temperature, in which the BCC phase was believed to have only refractory elements MoNbTaW while FCC carbide came from TaC and NbC. Carbides in the carbon doped MoNbTaW alloy were very stable since no phase transition was obtained even under 3.1 GPa and 870 °C by employing the resistor-heating diamond anvil cell (DAC) synchrotron X-ray diffraction technique. Via in situ examination, this study confirms the stability of carbides and MoNbTaW in the carbon doped CCA even under high pressure and high temperature.
... The resistively heated diamond anvil cell (RH-DAC) [131][132][133][134][135][136][137][138] is a complementary technique to laser heating, albeit less widely used because of the generally lower temperatures obtained and the complexity that lies in preparing the DAC. In resistive heating, samples are heated by conduction with the heat source outside the sample chamber, either by an external furnace (maximum temperature around 700 K) or by a small heater close to the diamond anvils (where much higher temperatures can be achieved). ...
... Various RH-DAC techniques have been proposed that can provide temperatures above 1200 K and can be used for the melting of metals, for example gold [139]. These techniques are based on (a) graphite heaters [135,136,138], (b) Mo wires [140], (c) W filaments [134], (d) Re gasket heating [137], or (e) metal strips placed directly in the sample chamber (internal resistive heating, [139,[141][142][143]). The latter technique has been proven very effective, especially when the metal strip is the sample itself, and temperatures of almost 4000 K have been reached in a study of the Fe-Ni-Si system [143]. ...
The accurate determination of melting curves for transition metals is an intense topic within high pressure research, both because of the technical challenges included as well as the controversial data obtained from various experiments. This review presents the main static techniques that are used for melting studies, with a strong focus on the diamond anvil cell; it also explores the state of the art of melting detection methods and analyzes the major reasons for discrepancies in the determination of the melting curves of transition metals. The physics of the melting transition is also discussed.
... [1,2] for review). The RH-DAC reaches routinely temperatures up to 1400 K [3][4][5], while temperatures of up to 2000 K have been reported in a few experiments based on miniature heater techniques [6]. The RH-DAC is complementary to externally resistively and laser-heated DACs because it covers a temperature range from ambient to 1400 K that is difficult to fully access with these techniques. ...
... Different designs of internally heated DACs have been reported, including geometries where the heating element fully surrounds the diamonds and gasket [3][4][5][13][14][15][16], or miniature heaters that are contained between the diamond culets [6,[17][18][19][20][21][22][23]. Temperatures in excess of 2000 K at pressures up to 50 GPa have been reported for miniature heaters [6]. ...
The diamond anvil cell (DAC) is a fundamental device used to explore the properties of materials under extreme pressure and temperature (P/T) conditions. In the past years, simultaneous high P/T DAC experiments using the resistively heated DAC (RH-DAC) techniques have been developed for studying materials properties in a wide PT range. However, the mechanical instability of metallic gaskets used for sample confinement at high P/T conditions remains a limiting factor for exploiting the accessible P/T range of the RH-DAC. In this study, we present a new gasket configuration that overcomes these limitations. It is based on an amorphous boron-epoxy mixture inserted in a rhenium gasket. We show how these gasket inserts stabilize the sample chamber over a wide P/T range, allowing monitoring sample properties using X-ray diffraction and absorption spectroscopy up to 50 GPa and 1620 K.
... In the fluoX DAC, the sample chamber can be heated up to ϳ1000°C by radiation of tungsten coils. 18 Two coils 120°a part and 120°from the collimator ensure a low thermal gradient at the sample location. Temperature in the DAC is remotely monitored and controlled by a K-type thermocouple placed as close as possible to one furnace. ...
... Vacuum of ca. 10 −5 mbar is obtained with a turbo pump mounted directly on the top of the chamber for maximum efficiency. 18 The vacuum box is made in aluminum 6061®, compatible with a water circulation in the walls that maintains their temperature lower than 300 K. The vacuum box is equipped with three air cooled kapton® windows of 50 m thickness for the incident, diffracted and fluorescent beams, respectively. ...
We present a new diamond anvil cell (DAC), hereafter called the fluoX DAC, dedicated for x-ray fluorescence (XRF) analysis of trace elements in fluids under high pressure and high temperature to 10 GPa and 1273 K at least. This new setup has allowed measurement of Rb, Sr, Y, Zr, with concentrations of 50 ppm to 5.6 GPa and 1273 K. The characteristics of the fluoX DAC consist in an optimized shielding and collection geometry in order to reduce the background level in XRF spectrum. Consequently, minimum detection limits of 0.3 ppm were calculated for the abovementioned elements in this new setup. This new DAC setup coupled to the hard x-rays focusing beamline ID22 (ESRF, France) offers the possibility to analyze in situ at high pressure and high temperature, ppm level concentrations of heavy elements, rare earth elements, and first transition metals, which are of prime importance in geochemical processes. The fluoX DAC is also suitable to x-ray diffraction over the same high pressure-temperature range.
... After when a semiconductor material or metal absorbs the laser energy, the leading edge deposits that energy into the electrons, after which the excited electrons collide with each other and turn into phonons. The phonons are then heated and diffused so that they can be used to determine the lattice temperature [7,8]. The practical importance of the end result of laser treatment cannot be overemphasized. ...
Optical and photo-thermal effects have emerged in many fields, including thermal characterization, spectroscopy, transportation, and non-destructive examinations. In this study, the Moore-Gibson-Thompson (MGT) thermoelastic model is used to explore the photo-thermal coupling of an isotropic, homogeneous, semiconducting and thermomagnetic solid. The heat conduction law is modified to include the time derivative of fractional order and theoretically formulate the system of governing equations. Using the extended Mittag-Leffler functions as nonsingular kernels, the Atangana and Baleanu derivatives considers the features of fractional derivatives. As measured by an external reference frame, it is taken into account that the medium rotates with a constant angular velocity about the axis of symmetry. The cavity boundaries undergo thermal shock and time-varying heat flux. It has been shown that the Laplace transform method is a powerful technique for solving such problems that link the plasma and heat transfer with phase delays. It is finally aimed to describe the numerical results for changes in carrier density as a function of time and radial distance, temperature increment, strain, thermal stresses, and displacement using a photo-induced carrier with different values of physical relaxation time and fractional operator.
... The enlarged pressure and temperature uncertainty and non-negligible pressure drifts have adversely affected in situ measurements in the DACs at high pressure and high temperature (HPHT). [13][14][15][16] To cope with the issues induced by temperature, a variety of solutions have been proposed and used in HPHT experiments. Different temperature calibration techniques, such as the thermocouple 17,18 and black-body fluorescence 19 calibration techniques, have been utilized to minimize the temperature uncertainty in the HPHT experiments. ...
Temperature induced pressure drift in the diamond anvil cell (DAC) is a major issue in high-pressure high-temperature experiments. It is commonly acknowledged that these drifts originate from multiple factors, but no systematic descriptions have been made so far. By introducing an internal water-cooling system in the DAC, we have performed a systematic investigation into temperature induced pressure drifts to reveal the mechanism behind them and to find a proper experimental procedure to achieve minimal pressure variation in DAC’s heating experiment. It is revealed in this experiment that pressure variation during heating processes originates from multiple temperature related factors of the DAC. The variation itself can be considered as a rebalancing process of the compression forces on the sample chamber initiated by the disturbance caused by temperature elevation. It is possible to suppress pressure variation by maintaining the temperature of the DAC body at room temperature to ensure the consistency of compression on the sample chamber. At the same time, the best procedure for the heating experiments is to properly pre-heat the sample chamber equipped with the internal water-cooling system before performing the in situ measurements on the temperature-related properties at the pressurized and heated conditions. Our discovery provides a reliable procedure for the sample heating process in the DAC and helps resolve the complex mystery of the influence of the combination of pressure and temperature in high-pressure high-temperature experiments.
... Laser heating has the benefit of being both spatially and temporally localized. Additionally, by establishing thermal gradients, sample temperatures considerably above the sample chamber's capacity can be obtained, such as heated samples in diamond anvil cells [38,39]. ...
Photothermal spectroscopy is a method of measuring the optical absorption and thermal properties of semiconductor materials using high-sensitivity spectroscopic techniques. Heating occurs due to light, which is absorbed but not dissipated by emission. In this paper, a new model is provided that can be used to understand the process of optical thermal transfer and the interaction between elastic plasma waves and heat. The proposed photothermal model is described by the Moore–Gibson–Thompson heat equation. Using the proposed model, the thermal and photoacoustic effects in an infinite isotropic and homogeneous body with a cylindrical cavity of semiconductor material crossed into a fixed magnetic field and subjected to high-intensity laser heat flux were investigated. The inner surface of the cavity is considered to be traction-free, and the carrier density is photogenerated by a laser pulse heat flux that decays exponentially. The numerical calculations for the components of thermal stresses, displacement, temperature field, and carrier density are obtained using the Laplace transform approach. The propagation of heat, elastic, and plasma waves, as well as the distributions of each investigated field, were examined and explained. The comparison is also used to see how different thermal response features, such as thermal relaxation, laser pulse duration, and lifetime, affect the thermoelastic response.
... Laser heating has the benefit of being both spatially and temporally localized. Moreover, by establishing thermal gradients, sample temperatures, considerably above the sample's chamber capacity, can be obtained [3,4]. ...
This work presents an analytical approach to study the photothermal response of a functionally graded semiconducting thermoelastic half-space. The generalized thermoelastic heat conduction theory without energy dissipation is employed to extract the governing equations in which the properties of a half-space material are supposed to change in the longitudinal direction. In the context of photothermal transitional model, the interaction between heat-elastic plasma waves is described. The governing equations for the physical field variables are determined by Laplace transform procedure
in the physical domain. The distribution of each field variable as well as the spread of thermo-elastic plasma waves are plotted and discussed. Some illustrative examples are presented to determine the influence of characteristic parameters such as thermal relaxation and the power law (nonhomogeneity) index on the thermoelastic behavior of the considered medium. Finally, some interesting situations are derived from the current formulation.
... Laser heating has the benefit of being both spatially and temporally localized. Additionally, by establishing thermal gradients, sample temperatures considerably above the sample chamber's capacity can be obtained, such as heated samples in diamond anvil cells [3,4]. ...
The current study aims to introduce a new generalized photothermal model in which heat equation is described based on the Moore–Gibson–Thompson (MGT) equation. The thermo-optical transition process can be understood, and the interaction between elastic plasma waves and heat can be investigated and explained using the suggested model. The proposed model was used to investigate the thermal and photoacoustic effects in an infinitely constrained solid cylinder of semiconductor material that was crossed into a fixed magnetic field and subjected to a high-intensity laser heal flux. The Laplace transform technique is used to derive the numerical expressions for the components of thermal stresses, displacement, temperature field, and carrier density. The propagation of thermal, elastic, and plasma waves, as well as the distributions of each studied field, was investigated and described. The comparison is also used to evaluate the impact of thermoelastic response characteristics such as thermal relaxations, temperature frequency, and lifetime on the photo-thermoelastic response.
... In an RH-DAC, resistive elements can be placed either outside the cell, thereby heating the entire DAC assembly [118,219,220], or inside the cell surrounding the anvils to provide more localised heating [185,[221][222][223][224][225][226][227]. Temperatures are typically monitored via a thermocouple positioned close to the sample. ...
Under extreme conditions of high pressure and temperature, liquids can undergo substantial structural transformations as their atoms rearrange to minimise energy within a more confined volume. Understanding the structural response of liquids under extreme conditions is important across a variety of disciplines, from fundamental physics and exotic chemistry to materials and planetary science. In situ experiments and atomistic simulations can provide crucial insight into the nature of liquid-liquid phase transitions and the complex phase diagrams and melting relations of high-pressure materials. Structural changes in natural magmas at the high-pressures experienced in deep planetary interiors can have a profound impact on their physical properties, knowledge of which is important to inform geochemical models of magmatic processes. Generating the extreme conditions required to melt samples at high-pressure, whilst simultaneously measuring their liquid structure, is a considerable challenge. The measurement, analysis, and interpretation of structural data is further complicated by the inherent disordered nature of liquids at the atomic-scale. However, recent advances in high-pressure technology mean that liquid diffraction measurements are becoming more routinely feasible at synchrotron facilities around the world. This topical review examines methods for high pressure synchrotron x-ray diffraction of liquids and the wide variety of systems which have been studied by them, from simple liquid metals and their remarkable complex behaviour at high-pressure, to molecular-polymeric liquid-liquid transitions in pnicogen and chalcogen liquids, and density-driven structural transformations in water and silicate melts.
... scitation.org/journal/rsi such as those based on molybdenum, 19 nichrome, 20 tungsten, 21,22 platinum, 23 platinum-rhodium, 24,25 and other alloys 26 have conventionally been used for EHDAC experiments. The heating assembly consists of a coiled wire with a ceramic insulating shell that is placed around the diamond anvil. ...
Semiconductor-based heaters for diamond anvil cells (DACs) have advantages over metal wire heaters in terms of repeated use and the ability to reach higher temperatures. We introduce a cylindrical SiC heater for an externally heated DAC (EHDAC) that works satisfactorily at temperatures up to 1500 K and pressures around 90 GPa. The heater is reusable and inexpensive, and only slight modifications to the DAC are required to fit the heater. Experiments on melting of NaCl and gold are conducted at ambient pressure to test the temperature accuracy of the EHDAC system, and resistance measurements on iodine at high pressures and temperatures are performed to assess the heater assembly. These test runs show that a uniform and accurate temperature can be maintained by the EHDAC assembly, which has potential applications to a variety of transport property measurements.
... Graphite has been used as a resistive heater over the widest temperature range; 3 it has a large range of thermal stability, with a sublimation temperature of 3900 K. Nevertheless, it requires a highly reducing environment, and its softness and fragility have limited its usage. Platinum, 15 molybdenum, 16,17 platinum/rhodium, 12 and tungsten wires have all been used (at times in conjunction with vacuum chambers), 18,19 but these have seldom been deployed above 1300 K. 14 Here, we present a modular, user-friendly plug-and-play resistive heater that is durable and able to reach temperatures corresponding to Earth's upper mantle and transition zone pressures (1700 K) at corresponding pressures (∼25 GPa) and hence helps quantify properties of materials at these conditions. In this paper, we provide a technical description of our design and report an example study where we measure the pressure dependence of the thermal expansion coefficient in MgO. ...
Resistive heating of a sample in a diamond anvil cell (DAC) can generate a homogeneous temperature field across the sample chamber with reliable temperatures measured by a thermocouple. It is of importance in experiments aiming at exploring phase diagrams and quantifying thermoelastic properties of materials. Here, we present a ring-heater design developed for BX90 diamond anvil cells (DACs). It is made of a ring-shaped aluminum oxide holder hosting a tungsten wire coil inside and coupled with Ar + 2% H2 gas to prevent oxidation during experiment. This modular plug-and-play design enables in situ studies of samples via x-ray diffraction up to a temperature of 1700 K. Temperature in the BX90 sample volume as measured through a thermocouple was calibrated using the melting point of gold. As an application of this design, we report the thermal expansion coefficient of MgO at 9.5(1) GPa.
... However, the lack of temperature measurement accuracy is an ongoing problem [25]. Resistively heated diamond anvil cell (DAC) [27] controls the temperature by mounting an electrical heater with adjustable voltage and current out of the DAC body. In this case, the temperature inside DAC body can be easily controlled and measured. ...
In this work, the formation of carbide with the concertation of carbon at 0.1 at.% in refractory high-entropy alloy (RHEA) Mo15Nb20Re15Ta30W20 was studied under both ambient and high-pressure high-temperature conditions. The x-ray diffraction of dilute carbon (C)-doped RHEA under ambient pressure showed that the phases and lattice constant of RHEA were not influenced by the addition of 0.1 at.% C. In contrast, C-doped RHEA showed unexpected phase formation and transformation under combined high-pressure and high-temperature conditions by resistively employing the heated diamond anvil cell (DAC) technique. The new FCC_L12 phase appeared at 6 GPa and 809 ℃ and preserved the ambient temperature and pressure. High-pressure and high-temperature promoted the formation of carbides Ta3C and Nb3C, which are stable and may further improve the mechanical performance of the dilute C-doped alloy Mo15Nb20Re15Ta30W20.
... External resistive heaters provide homogeneous heating in the sample region but they show important limitations in the temperature range (usually less than 900 K, under inert gas or vacuum conditions) and in the heating/cooling rates that are extremely slow (Schiferl, 1987). Several improved designs have been proposed to extend the temperature range up to 1500 K using also internal heaters around the diamond anvils (Liermann et al., 2009;Rekhi et al., 1999;Du et al., 2013;Pasternak et al., 2008). In this communication we present a new design and some preliminary results of an internally heated DAC suitable for in-situ high pressure measurements along fast heating and cooling cycles. ...
X-ray absorption spectroscopy (XAS) is presently a powerful and established tool to investigate solid and liquid matter at high pressure and high temperature (HP-HT). HP-HT XAS experiments rely on high pressure technology whose continuous development has extended the achievable range up to 100 GPa and more. In high pressure devices, high temperature conditions are typically obtained by using internal and external resistive heaters or by laser heating. We have recently developed a novel design for an internally heated diamond anvil cell (DAC) allowing XAS measurements under controlled high temperature conditions (tested up to about 1300 K). The sample in the new device can be rapidly heated or cooled (seconds or less) so the cell is suitable for studying melting/crystallization dynamics when coupled with a time-resolved XAS setup (second and sub-second ranges). Here we describe the internally heated DAC device which has been realized and tested in experiments on pure selenium at the energy dispersive ODE beamline of Synchrotron SOLEIL. We also present results obtained in XAS experiments of elemental Se using a large volume Paris-Edinburgh press, as an example of the relevance of structural studies of matter under extreme conditions.
... Resistive heating techniques are usually used to reach 800 K-1000 K, sometimes 1200 K [19]. This temperature limitation contrasts with the temperatures that can be obtained with large volume presses (2500-2800 K), and this is due to the fact that the heater is most of the time not under pressure. ...
This review provides an overview of high pressure crystallography using synchrotron radiation. Such experiments concern most of the scientific domains (Physics, Chemistry, Biology, Earth Science, Material Science...). After a description of the most used high pressure apparatus and of the different techniques of diffraction, adapted to high pressure environment, we present few examples of scientific results, selected from these different scientific domains. The perspective opened by recent experimental developments is also discussed.
... In their study, the cell was flushed with 98% argon + 2% hydrogen gas. Heating in vacuum suppresses such reactions of diamond at least up to 1850 K (Herchen & Cappelli, 1991), allowing experiments using diamond-anvil cells up to 1200 K and 20 GPa (Pasternak et al., 2008) and 1273 K and 5.6 GPa (Petitgirard et al., 2009). High-quality diamonds (characterized by very low birefringence and dislocation density) are more expensive, but less likely to ...
... The LVPs used for XAS can reach pressures of 20 GPa and temperatures of 3000 K with resistive heating and are associated to a sample size of about 500 m. DACs can reach the multi Mbar regime and temperatures between 2 K with a cryostat [15], ∼1000 K with a resistive setup [16,17] and ∼ 5000 K with a laser heating setup [18,19]. To reach the highest pressure the sample size should not exceed 10 m, therefore the use of a DAC device is in general associated with an X-ray focusing element. ...
... In their study, the cell was flushed with 98% argon + 2% hydrogen gas. Heating in vacuum suppresses such reactions of diamond at least up to 1850 K (Herchen & Cappelli, 1991), allowing experiments using diamond-anvil cells up to 1200 K and 20 GPa (Pasternak et al., 2008) and 1273 K and 5.6 GPa (Petitgirard et al., 2009). High-quality diamonds (characterized by very low birefringence and dislocation density) are more expensive, but less likely to ...
In this chapter, we describe the hydrothermal diamond-anvil cell (HDAC), which is specifically designed for experiments on systems with aqueous fluids to temperatures up to ~1000°C and pressures up to a few GPa to tens of GPa. This cell permits optical observation of the sample and the in situ determination of properties by 'photon-in - photon-out' techniques such as Raman spectroscopy. Several methods for pressure measurement are discussed in detail including the Raman spectroscopic pressure sensors α-quartz, berlinite, zircon, cubic boron nitride (c-BN), and 13C-diamond, the fluorescence sensors ruby (α-Al2O3:Cr3+), Sm:YAG (Y3Al5O12:Sm3+) and SrB4O7:Sm2+, and measurements of phase-transition temperatures. Furthermore, we give an overview of published Raman spectroscopic studies of geological fluids to high pressures and temperatures, in which diamond anvil cells were applied.
Melting of solids is a fundamental natural phenomenon whose pressure dependence has been of interest for nearly a century. However, the temporal evolution of the molten phase under pressure has eluded measurements because of experimental challenges. By using the shock front as a fiducial, we investigated the time-dependent growth of the molten phase in shock-compressed germanium. In situ x-ray diffraction measurements at different times (1 to 6 nanoseconds) behind the shock front quantified the real-time growth of the liquid phase at several peak stresses. These results show that the characteristic time for melting in shock-compressed germanium decreases from ~7.2 nanoseconds at 35 gigapascals to less than 1 nanosecond at 42 gigapascals. Our melting kinetics results suggest the need to consider heterogeneous nucleation as a mechanism for shock-induced melting and provide an approach to measuring melting kinetics in shock-compressed solids.
According to recent research, the theoretical consequences of viscoelastic materials may be adequately described using fractional calculus. A novel model for the fractional time derivative of the Kelvin-Voigt type of viscoelastic semiconductor material has been provided in this study. The Atangana and Baleanu (AB) fractional derivatives operator is utilized, which employs the generalized Mittag–Leffler function as a nonlocal and non-singular kernel and respects all features of fractional derivatives. The Moore–Gibson–Thompson (MGT) photothermal heat transfer model has also been considered to explain the mechanism of photosensitive heat transfer and the interplay between plasma, elastic, and heat signals. This fractional model is used to explore thermal and photoacoustic interactions when an infinite viscoelastic rotating material with a circular cylindrical hole is exposed to a time-dependent variable heat in the presence of an axial constant magnetic field. The solutions of photothermal field variables are obtained using Laplace transform methods, and the technique of Fourier series expansions is applied to obtain the inversions. Results have been listed to examine how the fractional-order and mechanical viscoelastic relaxation parameters affect different photo-thermoelastic variables that have physical meaning.
We have developed a new internally heated diamond anvil cell (DAC) system for in situ high-pressure and high-temperature x-ray and optical experiments. We have adopted a self-heating W/Re gasket design allowing for both sample confinement and heating. This solution has been seldom used in the past but proved to be very efficient to reduce the size of the heating spot near the sample region, improving heating and cooling rates as compared to other resistive heating strategies. The system has been widely tested under high-temperature conditions by performing several thermal emission measurements. A robust relationship between electric power and average sample temperature inside the DAC has been established up to about 1500 K by a measurement campaign on different simple substances. A micro-Raman spectrometer was used for various in situ optical measurements and allowed us to map the temperature distribution of the sample. The distribution resulted to be uniform within the typical uncertainty of these measurements (5% at 1000 K). The high-temperature performances of the DAC were also verified in a series of XAS (x-ray absorption spectroscopy) experiments using both nano-polycrystalline and single-crystal diamond anvils. XAS measurements of germanium at 3.5 GPa were obtained in the 300 K–1300 K range, studying the melting transition and nucleation to the crystal phase. The achievable heating and cooling rates of the DAC were studied exploiting a XAS dispersive setup, collecting series of near-edge XAS spectra with sub-second time resolution. An original XAS-based dynamical temperature calibration procedure was developed and used to monitor the sample and diamond temperatures during the application of constant power cycles, indicating that heating and cooling rates in the 100 K/s range can be easily achieved using this device.
High temperature is of paramount importance in high pressure science. One of the leading tools in this respect is the resistively heated diamond anvil cell (DAC), where the heat is provided by small heaters, positioned close to the diamond/gasket/sample region (internally heated DAC, IHDAC) or by wrapping the DAC body into bigger heaters (externally heated DAC, EHDAC). Although IHDACs can reach sample temperatures higher than 1000 K, they are difficult to handle and the heater/diamond/gasket/sample region may be affected by strong thermal gradients potentially hindering accurate temperature measurements. Here we present a novel EHDAC, which overcomes these issues by uniquely joining: (i) high mechanical precision for multi-Mbar, (ii) high temperature alloys for operating to 1000 K, (iii) membrane or screw driven, easily switchable between each other, (iv) operation into a vacuum chamber, (v) uniform temperature, (vi) facile handling, and (vii) possibility to add internal heaters for achieving even higher temperatures.
A new diamond-anvil cell apparatus for in situ synchrotron X-ray diffraction measurements of liquids and glasses, at pressures from ambient to 5 GPa and temperatures from ambient to 1300 K, is reported. This portable setup enables in situ monitoring of the melting of complex compounds and the determination of the structure and properties of melts under moderately high pressure and high temperature conditions relevant to industrial processes and magmatic processes in the Earth's crust and shallow mantle. The device was constructed according to a modified Bassett-type hydrothermal diamond-anvil cell design with a large angular opening (θ = 95°). This paper reports the successful application of this device to record in situ synchrotron X-ray diffraction of liquid Ga and synthetic PbSiO 3 glass to 1100 K and 3 GPa.
The transparent conducting oxide, SnO 2 , is a promising optoelectronic material with predicted tailorable properties via pressure-mediated band gap opening. While such electronic properties are typically modeled assuming perfect crystallinity, disordering of the O sublattice under pressure is qualitatively known. Here a quantitative approach is thus employed, combining extended X-ray absorption fine-structure (EXAFS) spectroscopy with X-ray diffraction, to probe the extent of Sn—O bond anharmonicities in the high-pressure cubic (Pa\bar{3}) SnO 2 – formed as a single phase and annealed by CO 2 laser heating to 2648 ± 41 K at 44.5 GPa. This combinational study reveals and quantifies a large degree of disordering in the O sublattice, while the Sn lattice remains ordered. Moreover, this study describes implementation of direct laser heating of non-metallic samples by CO 2 laser alongside EXAFS, and the high quality of data which may be achieved at high pressures in a diamond anvil cell when appropriate thermal annealing is applied.
Pressure and temperature phase transitions of nanomaterials often differ significantly from those of their bulk parents, offering novel approaches for the engineering of original materials. The importance or even the dominance of surface atoms in the nanoworld enhances the effects of environment, geometry, and intercalation. In the present article, we explore the current knowledge of these effects, as evidenced in the high pressure phase diagrams of nanomaterials such as nanocrystals, carbon nanotubes, fullerites, graphene, and other 2D systems, as well as nanoporous structures like clathrates or zeolites. Recent advances and future challenges in the use of extreme thermodynamic conditions to develop new functional nanomaterials, composites, or devices will be reviewed, along with the specificities of the experimental environment required for these investigations.
Laser-heated diamond anvil cell (LHDAC) technique is a unique and powerful experimental tool for studying the phase behaviour of materials at thermodynamic conditions comparable to the Earth’s deep interior. Fine tuning of the two thermodynamic variables viz., pressure and temperature enables one to manipulate matter on an atomic scale leading to the synthesis of novel compounds or transformation of the properties of existing materials. In this article the details of an ytterbium doped fibre laser based LHDAC facility are presented. The advantages and excellent performance of the off-axis angular heating geometry is demonstrated through results of high pressure melting experiments on KBr up to 24 GPa and high temperature high pressure synthesis of γ-Mo2N carried out by laser heating molybdenum metal and molecular nitrogen at 7 GPa and 2000 K in a Mao–Bell type diamond anvil cell.
Subduction zones are the largest recycling systems of our planet. Subduction zones involve recycling of water from hydrated oceanic crust and lithosphere to the upper mantle. Water plays a key role in subduction zone processes, including plate tectonics, magma generation, elemental transport and earthquake generation. The chemical composition, H2O content of oceanic lithosphere sinking to the mantle, age and geometry of subducting oceanic slab are the main factors controlling subduction zone processes including dehydration.The principle aim of this dissertation is to investigate the regime of water release from subducting oceanic plate and the associated behavior of Fe and S in serpentinites, which are the main carriers of water into the slab. The experimental approach of my work allows one to compare chemical and mineral changes occurred during dehydration of serpentinites with different composition. A number of analytical techniques were applied to study the influence of bulk rock composition on the mineral chemistry of produced assemblages. The experimentally investigated pressure-temperature ranges, i.e. 2 GPa and 450-900C, are representative for hot subduction zones. The extrapolation to other common geothermal gradients was done through thermodynamic modeling. The investigated serpentinite compositions correspond to natural serpentinized peridotites described for oceanic lithosphere.Bulk Fe content was demonstrated to decrease thermal stability of antigorite by 25C on average. Dehydration of Fe-bearing serpentinites, consequently, occurs at lower temperatures compared to Fe-free assemblages. Dehydration reactions observed in Fe-free systems are univariant reactions, while in Fe-bearing systems, serpentinites dehydration appears over a range of temperature through divariant reactions. Moreover, the presence of Al in serpentinite stabilized clinochlore, which retains 15% water initial contain in serpentinite down to ~120km (820°C/2 GPa) within hot subduction. Such a dependence of serpentinite dehydration on bulk Fe and Al brings importance of considering not only geometry and the age of the slab, but also a composition of slab lithologies while modeling and interpreting processes in subduction zone. A comparison of the depths of serpentinite dehydration and seismicity revealed a strong correlation and therefore a potential contribution of water release to seismicity in the case of hot subduction zones (i.e., Chili type subduction).X-ray absorption spectroscopy measurements revealed a progressive reduction of Fe and S in investigated serpentinites. The bulk Fe3+/Fetotal ratio initially high in serpentinite is shown to decrease in anhydrous and higher temperature assemblages due to magnetite and Fe3+-bearing antigorite breakdown at <550°C and 700°C, respectively. The presence of pyrite in serpentinite, which transforms to pyrrhotite below 450°C, imposes a release of ¼ of initial sulfur, in H2S form. The presence of magnetite and pyrite in serpentinite, is crucial and responsible for the production of highly oxidized fluids and volatile sulfur species, which can be transported from the subducting slab into the mantle wedge. Application of results, obtained in the present study, to nature demonstrates that fluids rising from subducting slab are responsible for oxidation of overlying mantle, and in addition, magnetite and antigorite breakdown which occurs with at least 100°C difference may cause a release of chemically different fluids at shallow (low-T) and deep (high-T) parts of subduction.
The ability to remotely control
pressure in diamond anvil cells
(DACs) in accurate and consistent manner at room temperature, as well as at cryogenic and elevated temperatures, is crucial for effective and reliable operation of a high-pressure synchrotron facility such as High Pressure Collaborative Access Team (HPCAT). Over the last several years, a considerable effort has been made to develop instrumentation for remote and automated pressure
control in DACs during synchrotron experiments. We have designed and implemented an array of modular pneumatic (double-diaphragm), mechanical (gearboxes), and piezoelectric devices and their combinations for controlling
pressure and compression/decompression rate at various temperature conditions from 4 K in cryostats to several thousand Kelvin in laser-heated DACs. Because HPCAT is a user facility and diamond
cells for user experiments are typically provided by users, our development effort has been focused on creating different loading mechanisms and frames for a variety of existing and commonly used diamond
cells rather than designing specialized or dedicated diamond
cells with various drives. In this paper, we review the available instrumentation for remote static and dynamic pressure
control in DACs and show some examples of their applications to high pressure research.
The striking advances in high pressure techniques and in theoretical methods have boosted synchrotron radiation research at extreme conditions. This chapter introduces the basic tools and methods used and illustrates a few examples of applications in the fields of Physics, Geochemistry and Environmental Science.
We developed a high pressure
cell for the in situ study of the porosity of solids under high uniaxial strain using neutron small angle scattering. The cell comprises a hydraulically actioned piston and a main body equipped with two single-crystal sapphire windows allowing for the neutron scattering of the sample. The sample cavity is designed to allow for a large volume variation as expected when compressing highly porous materials. We also implemented a loading protocol to adapt an existing diamond anvil cell for the study of porous materials by X-ray small angle scattering under high pressure. The two techniques are complementary as the radiation beam and the applied pressure are in one case perpendicular to each other (neutron
cell) and in the other case parallel (X-ray
cell). We will illustrate the use of these two techniques in the study of lamellar porous systems up to a maximum pressure of 0.1 GPa and 0.3 GPa for the neutron and X-ray
cells, respectively. These devices allow obtaining information on the evolution of porosity with pressure in the pore dimension subdomain defined by the wave-numbers explored in the scattering process. The evolution with the applied load of such parameters as the fractal dimension of the pore-matrix interface or the apparent specific surface in expanded graphite and in expanded vermiculite is used to illustrate the use of the high pressure
cells.
Generation of homogeneous high temperatures in the diamond-anvil cell
(DAC) has been a great challenge over the past several decades. Aiming
to overcome the disadvantages of small heating areas (<30um) and
large temperature gradients (>100K/um) inherent in the laser-heated
DAC as well as the limited pressure range (<60GPa) in multi-anvil
press experiments, we have developed an externally resistive-heated DAC
to produce uniform high temperatures at high pressures. In this study,
we modify a previous design employing graphite sheets (Liermann et al.,
RSI, 2009) with a ring-shaped graphite heater. In a pilot run, we
successfully generated temperatures of ~1800 K at a pressure of 20 GPa
before the R-type thermocouple melted. These conditions can be extended
to higher temperatures and pressures with the use of a C-type
thermocouple or spectroradiometry to measure temperature. This technique
will open doors to studying material properties, particularly melting,
transport and elasticity at high temperatures and pressures.
We describe a reliable high performance resistive heating method developed for the membrane diamond anvil cell. This method generates homogenous high temperatures at high pressure in the whole sample for extended operation period. It relies on two mini coil heaters made of Pt-Rh alloy wire mounted around the diamond anvils and gasket, while temperature is monitored by two K-type thermocouples mounted near the sample. The sample, diamonds, and tungsten-carbide seats are thermally insulated from the piston and cylinder keeping the cell temperature below 750 K while the sample temperature is 1200 K. The cell with the heaters is placed in a vacuum oven to prevent oxidation and unnecessary heat loss. This assembly allows complete remote operation, ideally suited for experiments at synchrotron facilities. Capabilities of the setup are demonstrated for in situ Raman and synchrotron x-ray diffraction measurements. We show experimental measurements from isothermal compression at 900 K and 580 K to 100 GPa and 185 GPa, respectively, and quasi-isobaric compression at 95 GPa over 1000 K.
In order to generate homogeneous high temperatures at high pressures, a ring-shaped graphite heater has been developed to resistively heat diamond-anvil cell (DAC) samples up to 1300 K. By putting the heater in direct contact with the diamond anvils, this graphite heater design features the following advantages: (1) efficient heating: sample can be heated to 1300 K while the DAC body temperature remains less than 800 K, eliminating the requirement of a special alloy for the DAC; (2) compact design: the sample can be analyzed with in situ measurements, e.g., x-ray, optical, and electrical probes are possible. In particular, the side access of the heater allows for radial x-ray diffraction (XRD) measurements in addition to traditional axial XRD.
The melting curve of Mg, Mn, Cu, Ag, Au, Zn, Cd, Al, In, and Pb has been measured up to 12 GPa using a Bridgman-type cell. Melting at high-pressure was identified detecting discontinuities in the electrical resistance of the studied metals. The results are compared with previous experimental and theoretical studies when possible. A comparison with the Lindemann’s law predictions is also done. In particular we found that among the studied metals Pb has the steepest melting curve (dTM/dP = 78 K/GPa). In contrast, Mn has the flattest melting curve (dTM/dP = 29 K/GPa). The reported results suggest that the electronic structure of an element might play a key role in determining the pressure dependence of its melting curve.
We describe the results of ab initio molecular-dynamics simulations of liquid Ge at five temperatures ranging from 1250 to 2000 K. The electronic structure is calculated using the local-density approximation and generalized norm-conserving pseudopotentials. The calculations yield the pair correlation function, the static structure factor, the bond-angle distribution function, the electronic density of states, the atomic self-diffusion coefficient, and finally the ac conductivity. Near melting, the structure factor has the experimentally observed shoulder on the high-k side of the principal peak, which becomes progressively less distinct at higher temperatures. The bond-angle distribution function indicates the persistence of covalent bonding for shorter bond lengths in the liquid state. The electronic density of states is metallic at all the temperatures with a pseudogap at a binding energy of 4.6 eV. The diffusion constant shows a sharp rise between 1250 and 1500 K (1.2×10-4–2.0×10-4 cm2 s-1 ) and increases less rapidly at higher temperatures, to only 2.3×10-4 cm2 s-1 at 2000 K.
An internal resistive heater contained completely between the anvil faces of a diamond anvil cell has been used to conduct experiments up to 10 GPa and temperatures up to 3000 K. There is evidence that pressures up to 50 GPa can be achieved with smaller anvil faces and smaller heater assembly. The technique offers a very homogeneous temperature profile and excellent time stability for studying both metallic and nonmetallic materials. Temperature is measured by spectroradiometry as an image of the incandescent sample is projected onto the end of a fiber optic cable leading to a spectrometer. A very linear relationship between temperature and power provides accurate temperature measurements even when the temperature is below incandescence. The melting of gold determined by loss of diffraction peaks occurred at temperatures in good agreement with published values. In situ Raman spectra of SiO2 revealed the conversion of quartz to coesite. This method offers a larger heating volume with more stable and uniform temperature than laser heating techniques and at temperatures much greater than those that can be achieved by external resistive heating techniques. © 2003 American Institute of Physics.
The high-pressure melting behavior of different iron alloys was investigated using the classical synchrotron-based in situ X-ray diffraction techniques. As they offer specific advantages and dis-advantages, both energy-dispersive (EDX) and angle-dispersive (ADX) X-ray diffraction methods were performed at the BL04B1 beamline of SPring8 (Japan) and at the ID27-30 beamline of the ESRF (France), respectively. High-pressure vessels and pressure ranges investigated include the Paris– Edinburgh press from 2 to 17 GPa, the SPEED-1500 multi-anvil press from 10 to 27 GPa, and the laser-heated diamond anvil cell from 15 to 60 GPa. The onset of melting (at the solidus or eutectic temperature) can be easily detected using EDX because the grains start to rotate relative to the X-ray beam, which provokes rapid and drastic changes with time of the peak growth rate. Then, the degree of melting can be determined, using both EDX and ADX, from the intensity of diffuse X-ray scat-tering characteristic of the liquid phase. This diffuse contribution can be easily differentiated from the Compton diffusion of the pressure medium because they have different shapes in the diffraction patterns. Information about the composition and/or about the structure of the liquid phase can then be extracted from the shape of the diffuse X-ray scattering.
Zinc metal has been studied at high pressure using x-ray absorption spectroscopy. In order to investigate the role of the different degrees of hydrostaticity on the occurrence of structural anomalies following the electronic topological transition, two pressure transmitting media have been used. Results show that the electronic topological transition, if it exists, does not induce an anomaly in the local environment of compressed Zn as a function of hydrostatic pressure and any anomaly must be related to a loss of hydrostaticity of the pressure transmitting medium. The near-edge structures of the spectra, sensitive to variations in the electronic density of states above the Fermi level, do not show any evidence of electronic transition whatever pressure transmitting medium is used.
High pressure and high temperature angle-dispersive x-ray diffraction measurements on gadolinium were performed up to 93GPa and nearly 2500K using argon as pressure medium. Our room temperature measurements confirmed the transition pressures reported in a previous study carried out using nitrogen as pressure medium, solving former discrepancies found in the literature. A new phase was observed above 1200K between 39GPa and 52GPa . Additionally, the structure of the previously observed dfcc and post-dfcc phases was determined, being the space group symmetry of the post-dfcc phase (C2/m) , different from what was predicted before. Finally, the room temperature equation of state was determined for Gd and its pressure-temperature phase diagram redefined.
A new double-sided laser heating system optimized for monochromatic X-ray diffraction at high pressure and high temperature has been developed at beamline ID27 of the European Synchrotron Radiation Facility (ESRF). The main components of this system including optimized focusing optics to produce a large and homogenous heated area, optimized mirror optics for temperature measurements and a state-of-the-art diffraction setup are described in details. Preliminary data collected at high pressure and high temperature on tungsten and iron are presented.
New diamond anvils with conical support are introduced. Compared to conventional anvils the new design offers superior alignment stability, larger aperture, and reduced cost owing to significantly smaller anvil diameters. Except for table and culet, all surfaces are precision ground on a lathe, which lowers cost compared to faceted anvils. The conical design allows for steel supports, which are significantly easier and cheaper to manufacture than tungsten carbide supports. Conical support also prevents seat damage upon diamond failure. An additional new feature of the anvils is the roughened outer portion of the culet, which increases friction between the anvils and the gasket. This increases the height to diameter ratio of the pressure cell and prevents bonding between gasket and diamond, which causes ring cracks during pressure release. This technique replaces complicated diamond coating procedures. The anvils have been extensively tested for culets ranging from 0.1 to 1 mm diameter up to megabar pressures. A new anvil shape with cup-shaped culets to further increase the cell volume and gasket stability is also introduced.
A detailed experimental investigation of the short-range structural properties in condensed phases of germanium is presented. X-ray-absorption measurements at the Ge K edge have been collected in a wide temperature range for different samples. Polycrystalline c-Ge was measured at 77, 296, 450, 620, 782, 920, and 1110 K, close to the Ge melting-point temperature ${\mathit{T}}_{\mathit{m}}$=1210.4 K. Evaporated amorphous Ge was measured at 297 K. Eight independent measurements for liquid germanium have been collected from about 950 K in highly supercooled conditions up to about 1600 K. The spectra show a remarkable temperature trend. By comparison, previous diffraction measurements on l-Ge were limited to two narrow temperature regions only, either above ${\mathit{T}}_{\mathit{m}}$ or around 1500 K, and no measurements in the supercooled liquid region existed. Data analysis has been performed with the GNXAS approach and account has been taken for the presence of double-excitation channels involving 3d and 3p electrons in addition to the 1s. The c-Ge structural results are found in excellent agreement with the known properties. The expansion of the average bond length R is in agreement with thermal expansion data. Mean-square vibrational amplitudes are in excellent agreement with both previous measurements and calculations in the harmonic approximation. The analysis of the signal in liquid Ge has been performed using a technique that allows to extract information on the radial distribution function g(r) directly comparable with molecular dynamics (MD) simulations or previous diffraction determinations.
We report the results of an extensive molecular-dynamics study of diffusion in liquid Si and Ge (l-Si and l-Ge) and of impurities in l-Ge, using empirical Stillinger-Weber (SW) potentials with several choices of parameters. We use a numerical algorithm in which the three-body part of the SW potential is decomposed into products of two-body potentials, thereby permitting the study of large systems. One choice of SW parameters agrees very well with the observed l-Ge structure factors. The diffusion coefficients D(T) at melting are found to be approximately 6.4×10-5 cm2/s for l-Si, in good agreement with previous calculations, and about 4.2×10-5 and 4.6×10-5 cm2/s for two models of l-Ge. In all cases, D(T) can be fitted to an activated temperature dependence, with activation energies Ed of about 0.42 eV for l-Si, and 0.32 or 0.26 eV for two models of l-Ge, as calculated from either the Einstein relation or from a Green-Kubo-type integration of the velocity autocorrelation function. D(T) for Si impurities in l-Ge is found to be very similar to the self-diffusion coefficient of l-Ge. We briefly discuss possible reasons why the SW potentials give D(T)’s substantially lower than ab initio predictions. © 1996 The American Physical Society.
Fe K-edge x-ray magnetic circular dichroism of magnetite (Fe3O4) powders was measured with synchrotron radiation under variable pressure and temperature conditions in diamond anvil cell. The magnetic dichroism was observed to decrease discontinuously by approximately 50% between 12 and 16 GPa, independent of temperature. The magnetic transition is attributed to a high-spin to intermediate-spin transition of Fe2+ ions in the octahedral sites and could account for previously observed structural and electrical anomalies in magnetite at this pressure range. The interpretation of x-ray magnetic circular dichroism data is supported by x-ray emission spectroscopy and theoretical cluster calculations.
Recently, a high-pressure x-ray diffraction study was performed on liquid germanium (l-Ge), in order to clarify the change in the local structure of a liquid under pressure. Inspired by this work, we perform tight-binding (TB) molecular dynamics simulations for l-Ge at seven different pressures. To this end, we construct a new TB scheme by modifying a previously reported nonorthogonal TB scheme. By explicitly taking into account the nonorthogonality of the atomic wave functions, we obtain a TB scheme which is accurate at both low and high pressures. The pair distribution function g(r), static structure factor S(Q), and bond-angle distribution function g(3)(rc,θ) are calculated, along with other quantities. The calculated g(r) and S(Q) are in excellent agreement with the above-mentioned experiments, which confirms the validity of our TB scheme. From a detailed analysis of atomic configurations, we elucidate the change in the local structure of l-Ge under pressure. We find that bonding in l-Ge is interpreted as a mixture of covalent and metallic bonding, and that as pressure increases, the ratio of covalent bonds decreases, although they still exist at pressures as high as 24.0 GPa. We further find that, by dividing g(3)(rc,θ) into covalent and isotropic parts, the covalent contribution to the local structure of l-Ge changes from a “disordered” β-Sn structure in the low-pressure region to a “pure” β-Sn structure in the high-pressure region.
We present a new experimental set-up for combined angle dispersive XRD and energy dispersive XAS measurements at high pressure successfully commissioned on the dispersive XAS beamline (ID24) at the ESRF. We illustrate preliminary results on a test experiment performed on ZnCl2 in the pressure and temperature range up to 6GPa and 650 K respectively. XAS at Zn K-edge and XRD data of three different phases of ZnCI2 are shown.
We have spectroradiometrically measured a suite of temperatures between 761 ± 128 and 7307 ± 958 K in the laser-heated diamond cell using Br2 sample material. Critical evaluation of each spectrum and the dataset as a whole in comparison with synthetic data confirms the high temperatures and demonstrates the observable effects of temperature gradients and wavelength-dependent emissivity or absorbance on a single spectrum. In addition, we quantitatively demonstrate the use of a sliding two-color pyrometer analysis to produce a consistent and meaningful estimate of uncertainty of spectral temperature measurements.
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Various structural investigations of liquid germanium have been reported up to now. However, these studies exhibit discrepancies on the coordination number. Therefore, we have performed a very precise measurement of the structure factor of liquid germanium at 1223K and 1473K using a 640-cell position sensitive detector. The coordination number is found to be nearly insensitive to the temperature. On the other hand, the obtained structure factors are compared with those deduced from both quasicrystalline and hard sphere type models in order to explain the strong change of the coordination number of the germanium at the melting point.
The present paper concerns a combined x-ray diffraction and absorption study of gallium phosphide (GaP) at high pressure up to 39 GPa. The aim of this study is twofold: To clarify the nature of the high pressure phase using x-ray diffraction and to determine the degree and the evolution of the short range chemical order using x-ray absorption. The analysis of x-ray diffraction shows that GaP transforms to a Cmcm structure and the absence of the “difference reflections” indicates that the Cmcm structure lacks long-range chemical order. In this system, the EXAFS is compatible with the hypothesis of a chemically ordered Cmcm local environment. The comparison between the XANES region of the spectra and multiple scattering calculations confirms this hypothesis, clearly showing that the Cmcm is short-range chemically ordered. The local environment of Ga is given by 6 P atoms and short-range Ga-Ga interactions are not likely to occur in this system, at least up to 39 GPa. This result shows that even in a compound with a relatively low ionicity of the bonds, this parameter dictates the short-range interactions up to very high pressures.
The equation of state of cubic boron nitride (cBN) has been determined to a maximum temperature of 3300 K at a simultaneous static pressure of up to more than 70 GPa. Ab initio calculations to 80 GPa and 2000 K have also been performed. Our experimental data can be reconciled with theoretical results and with the known thermal expansion at 1 bar if we assume a small increase in pressure during heating relative to that measured at ambient temperature. The present data combined with the Raman measurements we presented earlier form the basis of a high-temperature pressure scale that is good to at least 3300 K.
The local structure in deeply undercooled Ge has been probed by time-resolved x-ray-absorption spectroscopy (XAS). By using a technique that allows us to collect full x-ray-absorption spectra in less than a second, snapshots of the electronic and local structure in the metallic phase of Ge were taken at temperatures much lower than had been possible with previous static XAS investigations. Upon a rapid freezing of the melt, and prior to the occurrence of the solidification transition, we observe a sharpening of the pair correlation function g(r), and a slight shift of g(r) towards smaller distances. We interpret this phenomenon in terms of increased stability of the covalent bonds that are continuously formed and destroyed in the liquid.
The phase diagrams of Si and Ge have been investigated experimentally over a P, T range of about 200 kbar and 1000°C by observing electrical resistance behavior. For Si the boundary between the diamond cubic form and the metallic form extends from about 120 kbar at room temperature to about 150 kbar, 810°C, where melting occurs at the triple point. For Ge the corresponding boundary extends from about 115 kbar at room temperature to about 103 kbar, 600°C. A line drawn through the triple points for Sn, Ge, and Si, and extended, suggests that the diamond—metal—liquid triple point for carbon may be around 500 kbar, 2400°C. When the metallic forms are decompressed at room temperature they transform back to semiconducting forms different and more dense than the original diamond cubic forms. Upon heating these denser forms to a few hundred degrees at room pressure they transform to the usual diamond cubic forms. The absolute resistivity and temperature coefficient of resistance of metallic Ge has been determined.
The authors demonstrate that the cubic phase of quasibinary GeTe–Sb2Te3 alloys (GST), the material of choice in phase-change optical recording (such as digital versatile disk-random access memory) can be rendered amorphous by the application of hydrostatic pressure. The amorphization pressure depends on the GST composition. The pressure-induced amorphous phase possesses a local structure around Ge atoms similar to that of laser-amorphized GST. They argue that vacancies are crucial for the pressure-induced amorphization.
An external heating assemblage allowing diamond anvil cell (DAC) experiments at megabar pressures and temperatures above 1200 K was constructed. The complete high-pressure high-temperature system consists of an anvil assembly made from a special high-temperature alloy, a mechanical loading mechanism, and external resistive heaters placed around the cell. The new system allows fine adjustment of the pressure (within 1 GPa) over the whole temperature range. It maintains constant pressure (within 1 GPa at megabar pressures) and constant temperature (within 5 K at 1000 K) for several hours. Temperature is measured with an external thermocouple. The pressure chamber does not have a measurable temperature gradient. The new heating assemblage is easily coupled with a experimental setup at synchrotron radiation facilities and Raman spectrometers. We tested the performance of the new system by measuring the thermal expansion of Fe0.90Ni0.05 at different pressures and by studying phase transformations in TiO2 and the melting curve of H2O. © 2003 American Institute of Physics.
By in situ energy-dispersive X-ray absorption spectroscopy (EDXAS) and X-ray diffraction (XRD), we analyzed the evolution of niobium in a MgH2/Nb2O5 system based on high-energy ball milling during hydrogen cycling. The high time resolution of the EDXAS method allowed us to monitor fast sample changes during this process. Thereby, we demonstrated that the Nb2O5 is already partially reduced during the milling process with the MgH2. Further reduction occurs during the heating and cycling processes, in which a lower limit of oxidation state is reached. Hereby, a reaction between the niobium oxide and the Mg/MgH2 leads to a decrease of crystalline Nb2O5 and the formation of a ternary oxide phase MgxNbyO. During the cycling processes a repetitive Nb oxidation−reduction process was observed, which may indicate hydrogen diffusion along the ternary oxide by the formation of metastable niobium hydrides. This points to a mechanism of kinetic sorption improvement by diffusion of hydrogen through pathways of ternary Mg−Nb oxides, which may also reduce the activation energy of the Mg−MgH2 transition.
In-situ high pressure (up to 20 GPa) energy-dispersive EXAFS as well as energy- and angle-disper sive powder diffraction have been used to study phase transformations in bulk amorphous GaSb and (GaSb)(1-x)(Ge-2)(x). Complex transitional behavior was observed. The amorphous-to-high pressure crystalline GaSb II phase transition starts at a pressure of approximate to 4 GPa, whereas the analogous transition in crystalline GaSb takes place at around 7 GPa. The abnormally large Debye-Waller factor for Ga nearest neighbors in the high pressure phase is interpreted in terms of the existence of an orthorhombic structure. In the solid solutions of GaSb with Ge the transition pressure shifts to higher values with increasing Ge concentration x.
The present paper concerns x-ray absorption spectroscopy experiments at the As K-edge on
InAs up to 80 GPa. The aim of this study is to obtain quantitative information on the local
environment of As in the post-NaCl phases of InAs. These measurements confirm the
absence of the CsCl phase, and the analysis of the fine structure of the x-ray absorption
allows us to characterize the local structure of the high pressure phases of InAs
from their onset of appearance. While the Cmcm phase is locally very similar to
the NaCl structure, having a first coordination shell of six indium atoms, above
31 GPa an increasing number of As atoms are detected within a distance of 3.16 Å.
The atomic-scale structures of liquid Si, Ge and Sn have been modelled by the reverse Monte Carlo method. A geometrical analysis of the model atomic configurations has been carried out in terms of bond angle distributions and spherical harmonics invariants. Similar geometrical features, including signatures of local tetrahedral order, have been found in the first coordination shells of all the liquid metals studied. A relation between the local atomic ordering in liquid Si, Ge and Sn, and that of the corresponding solids with the tetrahedral white-tin-type structure has been established. The influence of the local and medium-range atomic orderings in liquid Se, Ge and Sn on the shape of the respective structure factors has been discussed.
The P-V and T-V equations of state of a natural biotite sample (Mg/Fe ratio approximate to 1) have been studied using in-situ high-pressure (0.000 1-11 GPa) synchrotron radiation powder diffraction at the European Synchrotron Radiation Facilities (ESRF) in Grenoble, France, and in-situ high-temperature (298-610 K) laboratory X-ray powder diffraction. A third-order Birch-Mumaghan model [V-0 = 498.7(l) angstrom(3), measured value] provides the following elastic parameters: K-0 = 49(l) GPa, K = 8.1(5). The volume thermal expansion is satisfactorily described by a constant value resulting in 37(2) 10(-6) K-1. Mossbauer spectroscopy proves that REDOX reactions have occurred upon heating, presumably 2(OH- + Fe+) -> 2O(2-) + 2Fe(3+) + H-2(up arrow) and/or 4Fe(2+) + 2OH(-) + O-2 -> 4Fe" + 3O(2-) + H2O. On the basis of the elastic and thermal parameters measured we have modeled the deformation contribution (G(deform)) to the Gibbs energy. The third-order Birch-Mumaghan model with V0 fixed at its experimental value and the model with refined V-0 do not significantly differ from one another in terms of G(deform). A comparison based on G(deform) between biotite and phlogopite shows a better compliance to P of the former, though balanced in mineral reactions by a difference of molar volume, i.e., V-0(biotite) > V-0(phlogopite).
X-ray Raman scattering experiments were performed on C60 fullerenes and multi-wall carbon nanotubes (MWCNT) up to 20 GPa and 25 GPa using a diamond anvil cell and synchrotron radiation at HPCAT, Advanced Photon Source. The intensity of the near edge peaks representing sp2 hybridization (π⁎) decreases with increasing pressure in both materials. Around 13 GPa the X-ray Raman spectra of C60 completely transformed to sp3 type bonding leading to diamond-like phase. Similar features have been observed in MWCNT at 16 GPa indicating the formation of strong interlayer covalent bonds. Our experiments are in excellent agreement with recent theoretical simulations reported on the mechanical behaviour of compressed nanotubes and provide direct experimental evidence for bond switching of these carbonaceous systems at high pressures.
This paper presents a new calibration of the pressure shift of the <sup>7</sup>D<sub>0</sub>-<sup>5</sup>F<sub>0</sub> fluorescence line of SrB <sub>4</sub> O <sub>7</sub> :Sm <sup>2+</sup> , in hydrostatic medium (helium) up to 124 GPa and in nonhydrostatic medium (H <sub>2</sub> O) up to 130 GPa. There is no quenching of the luminescence, in contrast to that observed in similar compounds. We show that this line permits more accurate pressure measurements at very high pressure than the commonly used R<sub>1</sub> emission line of ruby because it remains intense, sharp, well isolated from the other lines, and weakly dependent on nonhydrostaticity. The wavelength pressure shift of the <sup>7</sup>D<sub>0</sub>-<sup>5</sup>F<sub>0</sub> line is found to be very well represented by the nonlinear relation: P=4.032Δλ(1+9.29×10<sup>-3</sup>Δλ)/(1+2.32×10<sup>-2</sup>Δλ) with P in GPa and Δλ=λ-685.41 in nm. High temperature experiments up to 900 K at room pressure were also performed. The negligible temperature dependence and the small thermal line broadening are further advantages for high pressure–high temperature studies in diamond anvil cells. A metrology for in situ measurements of pressure and temperature, based on the combined use of this compound with ruby is also presented, along with a new calibration of the ruby R<sub>1</sub> frequency shift with temperature from 300 to 800 K. © 1997 American Institute of Physics.
A modular system of techniques and software has been developed for the calibration and correction of intensity linearity, uniformity of response, spatial distortion, and image plate decay. With calibration the Molecular Dynamics<sup>T</sup><sup>M</sup> Imaging Plate scanner system has been shown to give comparable results to the MarResearch<sup>T</sup><sup>M</sup> scanner. The ESRF x‐ray image intensifier/charge‐coupled device detectors inherently cause large spatial and uniformity of response distortions, and successful data analysis depends on calibration and correction. Results of synchrotron radiation experiments are presented. © 1995 American Institute of Physics.
A large optical‐aperture membrane diamond anvil cell designed for infrared spectroscopy is described. The cell offers definite advantages compared to existing systems. Other possibilities concerning x‐ray diffraction analyses with the cells are mentioned. © 1995 American Institute of Physics.
An energy-dispersive X-ray diffraction study on molten germanium has been carried out at temperatures of 1253 and 1503 K. The interference and atomic distribution functions were compared with model ones by considering the characteristic features found in crystal structures of solid germanium. It has been established that over the temperature interval presently investigated the essential structural features of molten germanium are likely to be described by the atomic arrangement of the tetrahedral type encountered in the high-pressure form of solid germanium with minor modification.
The interpretation of seismic data and computer modeling requires increased accuracy in relevant material properties in order to improve our knowledge of the structure and dynamics of the Earth's deep interior. To obtain such properties, a complementary method to classic shock compression experiments and theoretical calculations is the use of laser-heated diamond cells, which are now producing accurate data on phase diagrams, equations of state, and melting. Data on one of the most important measurements, the melting temperatures of iron at very high pressure, are now converging. Two other issues linking core properties to those of iron are investigated in the diamond cell: One is the melting point depression of iron in the presence of light elements, and the other is the structure of iron at the conditions of the inner core. First measurements on eutectic systems indicate a significant decrease in the melting point depression with increasing pressure, which is in contrast to previous predictions. X-ray diffraction measurements at simultaneously high pressure and high temperature have improved significantly with the installation of high-pressure ``beam lines'' at synchrotron facilities, and structural measurements on iron are in progress. Considerable efforts have been made to develop new techniques to heat minerals at the conditions of the deep mantle in the diamond cell and to measure their phase relations reliably. Even measurements of the melting behavior of realistic rock compositions at high pressure, previously considered to be impossible in the diamond cell, have been reported. The extrapolated solidus of the lower mantle intersects the geotherm at the core-mantle boundary, which may explain the seismically observed ultra low velocity zone. The diamond cell has great potential for future development and broad application, as new measurements on high-pressure geochemistry at deep mantle and core conditions have opened a new field of research. There are, however, strict experimental requirements for obtaining reliable data, which are summarized in the present paper. Results from recent measurements of melting temperatures and phase diagrams of lower mantle and core materials at very high pressure are reviewed.
We present results of a first-principles molecular-dynamics study of structural, dynamical, and electronic properties of liquid Ge. In agreement with experiments, the electronic density of states shows that liquid Ge is metallic. However, an analysis of the electronic charge density, pair correlation function, and structure factor shows the existence of some covalent bonds in the liquid. These bonds give rise to broad bands in the power spectrum, reminiscent of the vibrational modes of crystalline Ge. They are also responsible for the low coordination number found in the melt. The calculated diffusion coefficient is also in agreement with available experimental results.
In situ high-pressure x-ray-absorption spectra have been performed on amorphous and crystalline GeO2 using a diamond-anvil cell adapted to ane energy-dispersive spectrometer. The coordination of Ge changes from fourfold to sixfold at pressures between 7 and 9 GPa. The progressive evolution of the measured Ge-O distances as well as the modification in the x-ray-absorption near-edge structure indicate two different sites rather than a progressive site modification. The phase transition observed in the amorphous phase is reversible in contrast to that observed in the crystalline form.
A new facility for simultaneous extended X-ray absorption of fine structure (EXAFS), X-ray diffraction and photoluminescence measurements under high pressures has been developed for use on station 9.3 at the Daresbury Laboratory Synchrotron Radiation Source. This high-pressure facility can be used at any suitable beamline at a synchrotron source. Full remote operation of the rig allows simultaneous collection of optical and structural data while varying the pressure. The set-up is very flexible and can be tailored for a particular experiment, such as time- or temperature-dependent measurements. A new approach to the collection of high-pressure EXAFS data is also presented. The approach significantly shortens the experimental times and allows a dramatic increase in the quality of EXAFS data collected. It also opens up the possibility for EXAFS data collection at any pressure which can be generated using a diamond cell. The high quality of data collected is demonstrated with a GaN case study. Particular attention will be paid to the use of energy-dispersive EXAFS and quick-scanning EXAFS techniques under pressure.
Solid bromine has been studied by x-ray absorption spectroscopy experiments up to a maximum pressure of 75 GPa. The data analysis of the extended fine structure reveals that the intramolecular distance first increases, reaching its maximum value at 25+/-5 GPa. From this value the intramolecular distance abruptly begins to decrease evidencing a nonpreviously observed phase transformation taking place at 25+/-5 GPa. A maximum variation of 0.08 A is observed at 65+/-5 GPa where again a phase transition occurs. This last transformation could correspond with the recently observed change to an incommensurate modulated phase. We discuss the possible generalization of the observed new phase transition at 25+/-5 GPa to the case of the other halogens.
A rapid, convenient technique for precision pressure measurement in the diamond-anvil high-pressure cell, which makes use of the sharp-line (R-line) luminescence of ruby, has been developed. The observed shift is -0.77 +/-0.03 reciprocal centimeters per kilobar for R(1) and -0.84+/- 0.03 reciprocal centimeters per kilobar for R(2) to lower energy and is approximately linear in the range studied (to 22 kilobars). Line-broadening has been observed in some instances and has been tentatively identified with nonhydrostatic conditions surrounding the ruby sample.
We performed high-resolution inelastic x-ray scattering measurements on a single crystal of hcp cobalt at simultaneous high pressure and high temperature, obtaining 4 of the 5 independent elements of the elastic tensor. Our experiments indicate that the elasticity of hcp-Co is well described within the quasiharmonic approximation and that anharmonic high-temperature effects on the elastic moduli, sound velocities, and elastic anisotropy are minimal at constant density. These results support the validity of Birch's law and represent an important benchmark for ab initio thermal lattice dynamics and molecular-dynamics simulations.
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Heated DAC for HP/HT studies Rev. Sci. Instrum. 79, 085103 ͑2008͒ This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 136.165.238.131 On: Fri, 19 Dec 2014 23:50:44
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