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(color online). The relative density change (ρ=ρ 0 ) as functions of the relative PDP position change (q 1 =q 1 0 ) for three BMG samples: L62 (blue diamonds), La 62 Al 14 Co 10.83 Ni 10.83 Ag 2.34 (orange circles), and Cu 47 Ti 33 Zr 11 Ni 8 Nb 1 (magenta triangles). The lines represent the relationship ρ=ρ 0 ¼ ðq 1 =q 1 0 Þ D to guide the eye with different D values: D ¼ 3 (black dashed line), D ¼ 2.5 (blue dash-dotted line), D ¼ 2 (red dotted line). Three samples follow the5=2 power law very well. Thegray zone represents the region with D ¼ 2.5 AE 0.1.
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As a fundamental property of a material, density is controlled by the interatomic distances and the packing of microscopic constituents. The most prominent atomistic feature in a metallic glass (MG) that can be measured is its principal diffraction peak position (q_{1}) observable by x-ray, electron, or neutron diffraction, which is closely associa...
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Context 1
... that we have obtained both ρ (Fig. 3) and q 1 (Fig. 1) as a function of pressure, the relationship between ρ and q 1 can be simply established by transfer of variables. Figure 4 shows the density change (ρ=ρ 0 ) as a function of q 1 =q 1 0 for the L62 BMG sample. Indeed, the power law relation of ρ=ρ 0 ¼ ðq 1 =q 1 0 Þ D is strictly followed over the entire range of compression. ...
Context 2
... 10 up to 2.86 Å −1 , thus extending the range of q 1 almost to the limits of BMG (typically 2.1-2.9 Å −1 ). Surprisingly again, these two BMGs also closely fit the D ¼ 5=2 fractional power law relationship (Fig. 4) . The dotted line represents the fitting of density from ultrasonic measurement below 7.1 GPa using the third-order BM- EOS. The two density data sets collected using independent techniques are very consistent. PRL 112, 185502 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 9 MAY 2014 185502-3 compositions are available. ...
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Citations
... Compression in the 0-10 GPa range translates to a density variation from 5-20% in metallic glasses, depending on the bulk modulus of the glass (Zeng et al., 2014), to 34% in vitreous silica (Wakabayashi et al., 2011), and to a similar variation in chalcogenide glasses (Mei et al., 2006). Thus, the possibility to perform in situ XPCS under HP and HT truly allows us to investigate the effects of density on the dynamical properties of the structural glasses and their corresponding supercooled liquids, including the glass transition. ...
A new experimental setup combining X-ray photon correlation spectroscopy (XPCS) in the hard X-ray regime and a high-pressure sample environment has been developed to monitor the pressure dependence of the internal motion of complex systems down to the atomic scale in the multi-gigapascal range, from room temperature to 600 K. The high flux of coherent high-energy X-rays at fourth-generation synchrotron sources solves the problems caused by the absorption of diamond anvil cells used to generate high pressure, enabling the measurement of the intermediate scattering function over six orders of magnitude in time, from 10 ⁻³ s to 10 ³ s. The constraints posed by the high-pressure generation such as the preservation of X-ray coherence, as well as the sample, pressure and temperature stability, are discussed, and the feasibility of high-pressure XPCS is demonstrated through results obtained on metallic glasses.
... However, d = D in many glasses [30,32,33,31,34,35,36], which gives rise to controversies on its mechanism. Recent studies showed that pressure (or equivalently, density) and composition changes lead to different power laws. ...
... We generalize the power law Eq. (1) from glass [32,34,35] to liquid. q 1 in Eq. (1) is measured from the structure factor S(q) = N j=1 e iq·rj N k=1 e −iq·r k /N . ...
... d deviating from D has been observed in various metallic glasses under composition change [30,36] or glasses composed of particles with different softness under pressure change [32,35]. Such deviation manifests nonuniform deformations, but the type of deformation that can increase or decrease d is unclear [32,33]. ...
Characterizing the local structural evolution is an essential step in understanding the nature of glass transition. In this work, we probe the evolution of Voronoi cell geometry in simple glass models, and find that the individual particle cages deform anisotropically in supercooled liquid and isotropically in glass. We introduce an anisotropy parameter $k$ for each Voronoi cell, which mean value exhibits a sharp change at the mode-coupling glass transition $\phi_\mathrm{c}$. Moreover, a power law of packing fraction $\phi\propto q_1^{-d}$ is discovered in the liquid regime with $d>D$, in contrast to $d=D$ in the glass regime, where $q_1$ is the first peak position of structure factor, and $D$ is the space dimension. This power law is explained by the change of $k$. The active motions in supercooled liquid are spatially correlated with long axes rather than short axes of Voronoi cells. In addition, the dynamic slowing down approaching the glass transition can be well characterized through a modified free volume model based on $k$. These findings reveal that the nonagnostic structural parameter $k$ determines glassy dynamics and is effective in identifying the structure-dynamics correlations and the glass transition.
... Recently, the cluster packing of MGs was found to follow the self-similar rule on a fractal network with a dimension of 2.31, and later a dimensionality crossover at an intermediate length scale was suggested [5]. In particular, from the high pressure investigations of Ce-, La-, Cu-, and Ti-based MGs, it has been found that the density of an MG follows a 5/2 power of the FSDP position [38,48,49]. Here, we use both the cubic (3) and fractional noncubic (5/2) laws to estimate the relative volume change. ...
Comprehending the pressure/temperature induced structural transition in glasses, as one of the most fascinating issues in material science, is far away from being well understood. Here we report novel polyamorphic transitions in a Cu-based metallic glass (MG) with apparent nanoscale structure heterogeneity relating to the proper Y addition. The low-density MG compresses continuously with increasing pressure, and then a compression plateau appears after ~8.1 GPa, evolving into an intermediate state with an ultrahigh bulk modulus of ~467 GPa. And then it transforms to a high-density MG with significantly decreased structure heterogeneity above ~14.1 GPa. Three-dimensional atom probe tomography reveals concentration waves of Cu/Zr elements with an average wavelength of ~5-6 nm, which promote the formation of interconnected ring-like network composed of Cu-rich and Zr-rich dual-glass domains at nanometer scale. Our experimental and simulation results indicate that the step-like polyamorphism may stem from synergic effects of the abnormal compression of the Zr-Zr bond length at atomic scale and the interplay between the applied pressure and incipient concentration waves (Cu and Zr) at several nanometer scales. Present work provides new insights into polyamorphism in glasses, and contribute to developing high-performance amorphous materials by high-pressure nanostructure engineering.
... The position of the first diffraction peak (q 1 ) of the Zr(Hf) BMG is 2.632 Å − 1 by fitting the peak using a Gauss function and is slightly larger (by 0.15%) than that of the Zr(O) BMG, which is 2.628 Å − 1 . According to the power law between density and the q 1 [25,26], the density of the Zr(Hf) BMG would be Table 1 Contents of impurities in two zirconium raw materials measured by ICP-OES. The error is less than 1 ppm. ...
Minor alloying has been developed as an effective method to modify and optimize various properties of bulk metallic glasses (BMG). In this work, as inevitable minor alloying elements, two major impurities, hafnium (Hf) and oxygen (O) were quantitatively confirmed to co-exist in two zirconium (Zr) raw materials with different grades of impurities. The effects of these two impurities on the thermal properties, crystallization behavior, glass-forming ability (GFA), and mechanical properties of the nominal Zr 55 Cu 30 Al 10 Ni 5 BMG were systematically studied. The O impurity was found to promote the formation of the Al 5 Ni 3 Zr 2 intermetallic compound phase, which could account for the poor GFA, thermal stability, and plasticity associated with BMGs with higher O content in the Zr raw material. In contrast, although the impurity of Hf has a much higher content than O, a negligible effect of Hf on the Zr 55 Cu 30 Al 10 Ni 5 BMG was revealed. These findings were further confirmed by deliberately adding extra O and Hf with designed contents into the Zr 55 Cu 30 Al 10 Ni 5 BMG. Our results clarify the effects of different impurities in Zr raw materials on the Zr-based BMG and will help guide industrial production and applications of Zr-based BMGs.
... The annealed MG sample with less free volume is intuitively expected to be more incompressible than the as-spun MG sample, which is consistent with our experimental observation of the always larger q 1-annealed than q 1-as-spun in Fig. 4(a). The inverse XRD peak position q 1 is believed to correlate with the average atomic volume V a in MGs by a simple power-law relationship, i.e., V a ∝ (1/q 1 ) D [32], which thus could reflect the structural evolution with volume variance under pressure [33,34]. The exponent D of the power law varies in a narrow range below 3 depending on the specific composition. ...
... The exponent D of the power law varies in a narrow range below 3 depending on the specific composition. For the Zr-based MGs, D was experimentally determined to be ∼2.6 [33,34]. Therefore, the sample volume as a function of pressure can be estimated by V a ∝ (1/q 1 ) 2.6 for the Cu 46 Zr 46 Al 8 MG. ...
Free volume is one of the key structural concepts widely used to describe various glass phenomena. However,free volume is challenging to be rigorously defined in glass structures and directly determined by experiments.Here, we employed metallic glass as a simple glass model system and studied the structural evolution of anas-spun(hyperquenched) and another thermally annealed metallic glass with differentamounts of free volume by in situ high-pressure synchrotron x-ray diffraction. Therefore, the effect of free volume on the compression behavior of metallic glasses can be clarified by comparing the two samples at identical experimental conditions.
We find that a higher amount of free volume causes both lower density and bulk modulus as expected at ambientconditions.
... Moreover, the results of this study are consistent with the q2/q1(q2shoulder/q1) = As it is known, pressure is a strong and clear parameter that can reduce the volume (increase density) of materials. Changes in density or volume are known to be associated with the first strong peak shifts in both real and reciprocal space, which can be easily determined by the power law given as [54,55]; The values obtained for Cu60Ti20Zr20 are slightly higher than the Dfr1=2.50 [16,55,56] and Dfq1=2.52 [16], 2.54 [56] values previously reported for different glass systems. ...
During the rapid cooling process, the atomic structure of the Cu60Ti20Zr20 ternary alloy under external pressure was investigated by molecular dynamics simulations using the embedded atom method potential. The effect of the pressure was discussed in detail by using a variety of analysis methods. Glass transition temperature determined by the modified Wendt-Abraham parameter was found to increase with increasing pressure. It was observed that the calculated total (or partial) pair distribution function and structure factor are in good agreement with the experimental x-ray data (with the ab-initio molecular dynamics results). The bond angle distributions of Cu-centered triplets were more consistent with ideal icosahedral clusters than that of Ti- and Zr-centered triplets. The dominant clusters for all pressures were icosahedral-like clusters that were not much affected by pressure. In addition to the bonds between Cu–Zr pairs shortening more easily under high pressure than other pairs, it is found that the Cu60Ti20Zr20 glassy alloy remained stable under pressure and its topological and atomic structures did not change much with pressure.
... Although the density drops abruptly at 3.3 GPa on decompression when plotting against pressure, it falls in a linear behavior when plotting against k m in a log-log scale, as shown in the inset of the upper panel of figure 3. The line shows ρ ∼ k D m with D = 2.95 (16), which is larger than D = 5/2, characterizing the structure of soft metallic glasses [24]. The principal peak is originated from the spatial correlation of I atoms, which follows from the resultant partial structure factor of the RMC fit. ...
A molecular crystalline SnI4undergoes pressure-induced solid-state amorphization via molecular dissociation to the high-density amorphous (HDA) state, which we call Am-I. In the present study, we examine the reverse transition process from Am-I to the low-density amorphous (LDA) state, called Am-II. We first measure the structure factor on decompression from 30 GPa down to 1.1 GPa at room temperature, usingin situangle-dispersive synchrotron x-ray measurement and a diamond anvil cell. We then estimate the density, which exhibits an abrupt change between 3.3 and 3.0 GPa, indicating the HDA(Am-I)-to-LDA(Am-II) transition. We use the density and the molecular configuration generated from a molecular dynamics simulation as input to a reverse Monte Carlo fit. The fit vividly visualizes gradual molecular reassociation between 18 and 14 GPa within the Am-I region. The Am-I state can thus be divided into two states: the high-pressure Am-I state containing isolated Sn atoms and the low-pressure Am-I state consisting of deformed molecules connected by metallic I2bonds. In the latter state, the molecular shape becomesC3v-like just before the transition to Am-II, in which molecules recover the originalTdsymmetry. This local symmetry change has been detected on the liquid-liquid transition of SnI4, suggesting the strong coupling between the local symmetry and the global order parameter of density.
... Since the XRD patterns show anomalous changes rather than a simple densification effect during compression, the sample volume changes cannot be reliably estimated using the cubic power law. 41 By contrast, in situ high-pressure micro-Raman spectra of the silicone oil only exhibit continuous peak weakening and broadening from the beginning of compression, without any new peaks emerging during compression (Fig. 6). The recoverable peak profile after full pressure release to ∼0.2 GPa indicates that the structural changes in the silicone oil during compression are likely reversible. ...
A 4:1 (volume ratio) methanol–ethanol (ME) mixture and silicone oil are two of the most widely used liquid pressure-transmitting media (PTM) in high-pressure studies. Their hydrostatic limits have been extensively studied using various methods; however, the evolution of the atomic structures associated with their emerging nonhydrostaticity remains unclear. Here, we monitor their structures as functions of pressure up to ∼30 GPa at room temperature using in situ high-pressure synchrotron x-ray diffraction (XRD), optical micro-Raman spectroscopy, and ruby fluorescence spectroscopy in a diamond anvil cell. No crystallization is observed for either PTM. The pressure dependence of the principal diffraction peak position and width indicates the existence of a glass transition in the 4:1 ME mixture at ∼12 GPa and in the silicone oil at ∼3 GPa, beyond which a pressure gradient emerges and grows quickly with pressure. There may be another liquid-to-liquid transition in the 4:1 ME mixture at ∼5 GPa and two more glass-to-glass transitions in the silicone oil at ∼10 GPa and ∼16 GPa. By contrast, Raman signals only show peak weakening and broadening for typical structural disordering, and Raman spectroscopy seems to be less sensitive than XRD in catching these structural transitions related to hydrostaticity variations in both PTM. These results uncover rich pressure-induced transitions in the two PTM and clarify their effects on hydrostaticity with direct structural evidence. The high-pressure XRD and Raman data on the two PTM obtained in this work could also be helpful in distinguishing between signals from samples and those from PTM in future high-pressure experiments.
... [45] The average interatomic spacing in metallic glasses is directly linked to the material's density and free volume. [46,47] The calculated average interatomic spacings for the large intensity centers of gravity for DC and HiPIMS are 2.75 Å and 2.43 Å, respectively. The decrease in average atomic spacing of the HiPIMS film as compared to the DC film amounts to ~12%. ...
High-power impulse magnetron sputtering (HiPIMS) is a thin film deposition technique that combines the advantages of energetic deposition methods with magnetron sputtering. HiPIMS has so far mostly been utilized for the growth of crystalline coatings. Here we offer a study devoted to metallic glasses, in which we compare Zr60Cu25Al10Ni5 (target composition) thin films deposited by conventional direct current magnetron sputtering (DC) and HiPIMS. Film microstructure is strongly dependent on the choice of the sputtering method. The DC layers show a columnar structure with intra-columnar porosity, which provides a pathway for oxygen diffusion into the film. In contrast, HiPIMS films are column-free and possess about 4% higher density, as revealed by X-ray reflectivity. Electron diffraction reveals a decrease in average atomic spacing for the latter film of about 12%. These differences in film properties and morphology can be attributed to an increase in ad-atom mobility during HiPIMS caused by an increase in ion energy and flux of the film-forming species enabling a more efficient energy and momentum transfer to the growing film surface. The relative contribution of metallic and hence film forming ions to the overall ion flux of the DC plasma compared to the HiPIMS plasma is 13% and 96%, respectively. Additionally, a substrate bias causes the ionized film forming species during HiPIMS to arrive close to the substrate normal reducing shadowing effects. Different microstructures have a direct effect on the average roughness values, which for DC and HiPIMS films are 1.4 nm and 0.2 nm, respectively. The indentation hardness H and Young's modulus E are higher for the HiPIMS sample, at 9.2 ± 0.3 GPa and 131.6 ± 3.6 GPa, respectively. The increase in hardness for the HiPIMS sample as compared to the DC sample (~35%) can be attributed to higher film density, compressive (HiPIMS) as opposed to tensile (DC) stress and the lack of a columnar structure.
... Q 1 is related to the atomic volume in MG systems following a power-law relationship. 32,33 In this work, the 2.5 power-law [34][35][36] that was experimentally verified to relate Q 1 with volume under pressure in MGs was adopted to estimate the volume changes during compression. Figure 2 shows the relative volume, V P /V 0 = (Q 1_0 /Q 1_P ) 2,5 (where the subscripts 0 and P denote the initial-pressure and a given pressure, respectively), of Al 93 Ce 7 MG as a function of pressure. ...
Polyamorphism discovered in lanthanide-rich metallic glasses (MGs) has been attributed to the electronic transition of the lanthanide element as a solvent element. In this work, we report that pressure-induced polyamorphism still exists in a Ce-poor Al93Ce7 binary MG where the 4f electron element serves as a solute and solute–solute avoidance is expected. The polyamorphic transition, observed by in situ high-pressure synchrotron x-ray diffraction, is accompanied by a volume collapse of ∼0.78% and occurs over a narrow pressure range from ∼0.8 to ∼1.8 GPa. Further synchrotron Ce L3-edge x-ray absorption spectroscopy measurements reveal that pressure-induced 4f electron delocalization underlies the polyamorphic transition. Molecular dynamics simulations confirm that the Ce atoms in the MG are completely isolated by the solvent Al atoms. This result demonstrates that 4f element-bearing alloys with extremely dilute concentrations can also exhibit polyamorphic states originating from electronic transitions, extending the compositional space of polyamorphism of MGs into very dilute regions. Our work suggests that tunable properties under compressive stress could be achieved in MGs by even minor doping of elements prone to electronic transitions.
