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High-pressure and high-temperature x-ray absorption study of liquid and solid gallium
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Good quality extended x-ray absorption fine structure (EXAFS) spectra near the Ga K edge have been collected in wide pressure and temperature ranges (namely 0–16 GPa, 298–498 K) using the dispersive setup installed at the LURE synchrotron radiation facility and diamond anvil cell as pressure device. Energy dispersive x-ray diffraction data have been also measured in similar thermodynamical conditions. EXAFS spectra are shown to be sensitive to phase transitions occurring at high pressures and temperatures. Occurrence of stable and metastable phases and location of the coexistence lines are discussed in light of the results obtained using both experimental techniques. The phase diagram of pure gallium has been extended considering present experimental results. EXAFS data-analysis is performed using advanced ab initio methods (GNXAS). Accurate information about local structure in solid and liquid gallium at extreme conditions is obtained. The short-range two-body distribution functions are reconstructed by EXAFS for liquid and solid gallium as a function of pressure and temperature.
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... The red dots ( ) represent the thermodynamic conditions in the solid phase, while the blue dots ( ) represent the data points in the liquid phase. The black curve (-) is the melting line of elemental Ga [52], while the blue dashed line (---) represents a linear fit of the melting line of the eutectic GaIn established in the present study. The data points represented by other colors and shapes are from the isothermal XRD experiments of Q. Yu et al [23], in order to compare different results. ...
The structure of the Ga85.8 In14.2 eutectic liquid alloy has been investigated both under ambient conditions and at high pressure/high temperature using x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD) techniques. The local structure of the liquid alloy at ambient conditions was analyzed by using double-edge refinements of the XAS data. Solid-liquid phase transitions under high pressure and high temperature conditions were monitored by combined XAS and XRD measurements along several quasi-isobaric heating runs, allowing us to draw a melting line up to 10 GPa. The established melting line was found to be slightly below the one of pure gallium (Ga) and to follow its trend as expected from the eutectic nature of the compound. The series of Ga K-edge XAFS spectra measured at different pressures indicates the absence of large structural modifications at the local Ga sites in the liquid within the investigated pressure and temperature range.
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... The anomalously low melting temperature and negative melting curve of Ga means simply compressing the element in a pressure cell at ambient-T will cause it to melt, a trait which has been exploited in some low-p diffraction studies to ∼ 2 GPa made in an unheated DAC [307][308][309]. However, there is little deviation in the local structure of liquid Ga in this p-range by comparison with ambient-p measurements [310]. ...
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.
... Strong electronic bonding states exist between two Ga atoms forming a Ga pair, whereas the bonding energy between Ga pairs is significantly lower [20]. Besides the liquid phase of Ga, several different solid-state modifications of Ga exist and are referred to as αto γ -Ga phase occurring at defined pressure-temperature conditions [21] as well as in metastable supercooling phases [22,23]. The investigation of atomically thin Ga films on semiconducting substrates and their surface reconstruction behavior on these surfaces is still a matter of scientific studies [24]. ...
We demonstrate the fabrication of an ultrathin gallium film, also known as gallenene, beneath epitaxial graphene on 6H-SiC under ambient conditions triggered by liquid gallium intercalation. Gallenene has been fabricated using liquid metal intercalation, achieving lateral intercalation and diffusion of Ga atoms at room temperature on square centimeter areas limited only by the graphene samples’ size. The stepwise self-propagation of the gallenene film below the epitaxial graphene surface on the macroscopic scale was observed by optical microscopy shortly after the initial processing without further physical or chemical treatment. Directional Ga diffusion of gallenene occurs on SiC terraces since the terrace steps form an energetic barrier (Ehrlich-Schwoebel barrier), retarding the gallenene propagation. The subsequent conversion of the epitaxial graphene into quasi-free-standing bilayer graphene and the graphene-gallenene heterostack interactions have been analyzed by x-ray photoelectron spectroscopy and Raman measurements. The results reveal an alternative approach for the controlled fabrication of wafer-scale gallenene as well as for two-dimensional heterostructures and stacks based on the interaction between liquid metal and epitaxial graphene.
... The existence of a first-order liquid-liquid phase transition (LLPT) has been postulated [23][24][25][26] on the basis that other candidate polyamorphic liquids exhibit similar anomalous behavior [27], notably water [28], silicon [29], sulphur [30], and phosphorous [9]. Previous in situ structural measurements of liquid gallium at high p are limited to ∼6 GPa [26,[31][32][33][34][35][36][37] by synchrotron x-ray diffraction (SXRD) and 9 GPa by x-ray spectroscopy [38]. At ambient p and T m the average coordination numbern Ga Ga increases from 7 in the solid Ga-I phase to ∼10 [34], compared to a typical value of 11-12 in most liquid metals. ...
The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high pressure (p) and high temperature (T) up to 26 GPa and 900 K by in situ synchrotron x-ray diffraction. Ab initio molecular dynamics simulations up to 33.4 GPa and 1000 K are in excellent agreement with the experimental measurements, providing detailed insight at the level of pair distribution functions. The results reveal an absence of dimeric bonding in the liquid state and a continuous increase in average coordination number n¯GaGa from 10.4(2) at 0.1 GPa approaching ∼12 by 25 GPa. Topological cluster analysis of the simulation trajectories finds increasing fractions of fivefold symmetric and crystalline motifs at high p−T. Although the liquid progressively resembles a hard-sphere structure towards the melting curve, the deviation from this simple description remains large (≥40%) across all p−T space, with specific motifs of different geometries strongly correlating with low local two-body excess entropy at high p−T.
... Indeed, pressure is another parameter that may be exploited in active and phase-change plasmonics. Although several high-pressure stable Ga-phases have been reported in the literature (see Fig. 1) [1,17], i.e., Ga(II) (which according to Ref. [17] may coexists with β-Ga), Ga(III), Ga(IV), and Ga(V) [17,[20][21][22], none of these previous studies have presented the optical properties of these high-pressure Ga-phases. Furthermore, the relationship between pressure and phase becomes very relevant for nanoparticles, where, because of the curvature radius, R, the Laplace pressure (∆P = 2γ lv /R, being γ lv the liquid/vapor surface tension) inside the nanoparticle can reach very high values (of the order of GPa) and induce high pressure phases [18]. ...
In order to exploit gallium’s (Ga) rich polymorphism in the design of phase-change plasmonic systems, accurate understanding of the dielectric function of the different Ga-phases is crucial. The dielectric dispersion profiles of those phases appearing at atmospheric pressure have been reported in the literature, but there is no information on the dielectric function of the high-pressure Ga-phases. Through first principles calculations we present a comprehensive analysis of the interdependence of the crystal structure, band structure, and dielectric function of two high-pressure Ga phases (Ga(II) and Ga(III)). The plasmonic behavior of these high-pressure Ga-phases is compared to those stable (liquid- and α-Ga) and metastable (β-, γ- and δ-Ga) at atmospherics pressure. This analysis can have important implications in the design of pressure-driven phase-change Ga plasmonic devices and high-pressure SERS substrates.
The density of liquid metals at high pressure and high-temperature provides fundamental and important information for understanding their compression behavior and elastic properties. In this study, the densities of liquid gallium (Ga) were measured up to 10 GPa and 533 K using the X-ray absorption method combined with an externally heated diamond anvil cell. The elastic properties (the isothermal bulk modulus (KT0), and its pressure derivative (KT0’)) of liquid Ga were obtained by fitting the density data with three equations of state (EOSs) (Murnaghan, third order Birch–Murnaghan, and Vinet). The KT0 values of liquid Ga were determined to be 45.7 ± 1.0–51.7 ± 1.0 GPa at 500 K assuming KT0’ values of 4–6. The obtained KT0 or KT0′ showed almost the same values regardless of the EOS used. Compared with previous results, the compression curve of liquid Ga obtained in this study had a slightly stiffer trend at higher pressures.
In this study, the effects of high pressure ranging from 0 to 100 GPa on the structural evolution of liquid metallic Ti62Cu38 alloy during rapid cooling have been extensively investigated by using classical molecular dynamics simulation with embedded atom method at a cooling rate of 5 × 10¹⁰ K s⁻¹. To investigate the first order phase transition during the solidification of the system and to determine the crystallization and glass transition temperatures, the temperature-dependent change in the curves of thermodynamic properties such as average volume per atom, specific heat and enthalpy are examined. Structural properties are expressed by using pair distribution functions, structure factors and atomic configuration. The microstructural atomic order in the system are characterized by using Honeycutt-Andersen pairs and Voronoi tessellation analysis methods. The results provide convincing evidence that the applied pressure during rapid cooling has a strong effect on determining whether the metallic liquid Ti62Cu38 will transform into a crystal-like structure or a glassy structure. The critical pressure for the glass formation are predicted to be approximately 10 GPa. While the simulated crystallization and glass transition temperatures increase linear with a slope of 11.11 K GPa⁻¹ within the range of 0–9 GPa and with a slope of 12.10 K GPa⁻¹ within the range of 10–100 GPa, respectively. While crystal-like clusters are dominant in the system up to 10 GPa, icosahedral-like clusters representing a short range order at 10 GPa become dominant in the system. The amount of dominant icosahedral-like clusters remains basically stable with pressure increase from 10 to 100 GPa. Also, as the pressure is applied, the calculated bond lengths for all bond pairs decrease.
The structural evolutions and abnormal bonding ways of the Zr80Pt20 binary alloy during rapid solidification under different pressures from 0 to 120 GPa have been investigated by classical molecular dynamics simulations in conjunction with the embedding atom method. The pair distribution function, the coordination number, the Warren-Cowley parameter, the bond length and the pair analysis technique are used to reveal the structural evolution of the Zr80Pt20 solidified under normal and high pressures. Persuasive evidence indicates that the applied pressure strongly affects the vitrification (for 0 ≤ P ≤ 20 and 90 ≤ P ≤ 120 GPa) and crystallization (for 30 ≤ P ≤ 80 GPa) processes of the metallic liquid and causes significant changes in the microstructure of the system. Interestingly, we have observed that the crystallization for the Zr80Pt20 system is associated with volume expansion between 50 and 80 GPa, in contrast to the volume contraction observed under 30 and 40 GPa. The results of the atomic structure analysis show that there is an unexpected shortening of Zr-Zr bonds under high pressures, which is related to the change of the atomic packing in the Zr80Pt20 alloy from loose to dense with increasing pressure. The results of the analysis show that the bonds between Zr-Zr and Pt-Pt pairs can be shortened more easily than the bonds between Zr-Pt pairs at high pressures and also the clustering behaviors of Zr-Zr or Pt-Pt bonds reveals the presence of composition segregation. This study presents encouraging findings for the experimental investigation of glass transition and crystallization processes in Zr-Pt metallic liquids during rapid cooling and under high pressure.
Polyvalent metal melts (gallium, tin, bismuth, etc.) have microscopic structural features, which are detected by neutron and X-ray diffraction and which are absent in simple liquids. Based on neutron and X-ray diffraction data and results of ab initio molecular dynamics simulations for liquid gallium, we examine the structure of this liquid metal at atomistic level. Time-resolved cluster analysis allows one to reveal that the short-range structural order in liquid gallium is determined by a range of the correlation lengths. This analysis performed over set of independent samples corresponding to equilibrium liquid phase discloses that there are no stable crystalline domains as well as molecule-like Ga2 dimers typical for crystal phases of gallium. Structure of liquid gallium can be reproduced by the simplified model of the close-packed system of soft quasi-spheres. The results can be applied to analyze the fine structure of other polyvalent liquid metals.
Phase transitions in submicrometric Ga droplets confined in epoxy resin are studied by combining energy-dispersive x-ray diffraction (EDXRD), x-ray absorption fine structure, and single-energy x-ray absorption. The restricted fluid is undercooled down to 150 K while the melting point is depressed down to 254 K. Melting and freezing are sharp processes occurring with temperature broadening of 1 and 10 K, respectively. EDXRD patterns are consistent with that of beta-Ga, while the stable phase at ambient conditions alpha-Ga is not found to exist. Appearance of gamma-Ga and delta-Ga solid phases and relevance of present results to recent studies of Ga confined in porous glass are discussed.
Accurate extended x-ray absorption fine structure measurements of molten RbBr and CuBr are analyzed and compared with computer simulations and neutron diffraction results. Advanced multiple-edge ab initio methods are used for data analysis. The short-range cation-anion pair distribution function of liquid RbBr is found to be in agreement with previous molecular dynamic simulations confirming the accuracy of present theoretical models. In liquid CuBr, due to the exceptional short-range sensitivity, direct evidence for nearly covalent bonding is obtained, improving previous neutron diffraction determinations. Possible important consequences of present results for experimental studies of binary liquid systems are addressed.
Amorphous films of some μm in thickness, prepared by low temperature condensation in an ultra-high vacuum onto liquid helium cooled substrates, have been studied in situ by using an X-ray diffractometer operating in a symmetrical reflection mode. The structure factor of gallium has been obtained over the wavevector range 1.3 to 16.1 Å− by means of two wavelengths, CrKα and MoKα, monochromatized by balanced filters. The average number of nearest neighbours deduced from the well-resolved first maximum in the radial distribution function is equal to 9.3 atoms. The results are compared to those previously found by electron diffraction measurements on thin films and also to the structure of supercooled liquid.
The possibilities given by XAS for structural determination under extreme conditions are discussed through the example of HgTe which exhibits three phase transition below 20 GPa. All of the structures have been determined or corroborated using EXAFS analysis and XANES simulations. Pressure induced amorphization (berlinites) or crystallization (amorphous Ge and liquid Kr) can be followed by XAS before and after the transition. Future developments related to the new generation of synchrotron radiation sources are presented.
A high-pressure powder x-ray-diffraction experiment has been carried out
on Ga up to 150 GPa at room temperature. The c/a axial ratio of the
body-centered-tetragonal phase III continuously decreases with pressure
and becomes 2 at 120+/-10 GPa, where an fcc lattice is realized. There
is no detectable volume change at the phase transition. The fcc phase
Ga(IV) is stable to at least 150 GPa. Full-potential linearized
augmented plane-wave calculations have been done to investigate the
pressure dependence of the c/a axial ratio of phase III. The result of
the calculation is in reasonable agreement with the present experiment.
The energy band structure of fcc Ga has also been calculated with the
pseudopotential method. The valence bands are found to touch the 3d core
states at about 79 GPa.
The photodiode array provided a position sensitive detector for powerful X-ray sources. Then the development of the energy dispersive scheme for the X-ray absorption experiments became realistic. The data acquisition system and elements of optics are discussed. Experiments in transmission mode and in total reflection mode illustrate the dramatic gain in data acquisition time as well as advantages dealing with the focussing optics.
Aspects of the optics of the energy-dispersive scheme for X-ray absorption spectroscopy are discussed. The idea of a set of monochromatic focus points related to a set of local Rowland circles is introduced to account for the source-size effect on the energy resolution. It is shown that there exists an optimized location of the position-sensitive detector where the energy resolution is no longer source-size dependent. In addition, the stability of the dispersive optical system has been estimated and a 10 meV energy-scale reliability is currently achieved.
The elemental metals Ga and Tl are studied under pressure in a diamond anvil cell by energy dispersive x-ray diffraction. While Tl remains in the high-pressure cF4 structure up to the highest pressures achieved, several phase transitions are observed in Ga. Different equation-of-state (EOS) forms are fitted to the experimental data. A detailed analysis of the data shows that a simple first-order EOS form can describe the isothermal pressure-volume behavior of all the phases for Ga as well as for Tl. Furthermore, a comparison of the structural behavior under pressure is made for all the group-IIIA elements of the Periodic Table.
The first report of an X-ray absorption spectroscopy (XAS) study of liquid gallium, carried out at several temperatures in liquid and crystalline phases and in the supercooled state, is presented. Data analysis has shown the presence of two resolved first-neighbour distances and a detectable signal due to three-body configurations.