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We utilized the pair distribution function method to characterize the pressure-induced polyamorphic transition in Ce60Al20Cu20 and Ce55Al45 metallic glass at room temperature. Using synchrotron high-energy x-ray diffraction we collected scattering information from a large Q-space coverage, which in turn gave a high resolution g(r) that provided accurate local structure information. We observed a sudden change in compressibility and the nearest neighbor distance at 3.50–6.32 GPa for Ce60Al20Cu20 and 2.20–6.89 GPa for Ce55Al45. The origin of the volume collapse seemed to be pressure-induced qualitative changes in bond shortening that corresponded to different coordination spheres. The polyamorphic transitions in these two systems from low-density glass (LDG) to high-density glass (HDG) are associated with local atomic rearrangements.

Compressional behavior of a natural hypersthene has been investigated at pressures up to 10.1 GPa at room temperature using in situ synchrotron X-ray diffraction in a diamond anvil cell. No phase transition was observed within the experimental pressure range. The pressure–volume data have been fitted with a third-order Birch–Murnaghan equation of state, resulting in K0 = 113.6(6.2) GPa and K0′=7.7(2.0) for the bulk modulus and its pressure derivative with a fixed unit-cell volume V0 = 854.0(6) A3. The unit-cell parameters, a, b, and c, decrease nonlinearly with elevated pressure and show an anisotropic axial compressibility with a ratio βa: βb: βc: =1:2.05:1.3. The comparison with previous results of orthopyroxene reveals that Al substitution causes a decrease in unit-cell volume and an increase in the bulk modulus, whereas the incorporation of Fe has opposite effects. The relation between unit-cell volume and En/Ts contents has been obtained, V0 (A3) = 873.7(1.1) − 40.8(1.44) × En-90.6(14.7) ×...

Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic ulvospinel (Fe1.94Ti0.03)Ti1.00O4.00 has been investigated up to about 7.05 GPa at 300 K. The pressure–volume data fitted to the second-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (K T ) of 147(4) GPa (K′ T fixed as 4). This value is slightly larger than that previously determined by an ultrasonic pulse echo method (121(2) GPa; Syono et al., J Phys Soc Jpn 31:471–476, 1971), but substantially smaller than that recently determined by a synchrotron X-ray diffraction technique (251(3) GPa; Yamanaka et al., Phys Rev B 80:134120, 2009; Am Mineral 98:736–744, 2013). Combined with the K T of magnetite (Fe3O4; ~182(3) GPa), our finding suggests that the bulk modulus of the solid solutions Fe3−x Ti x O4 (0 ≤ x ≤ 1) along the join magnetite–ulvospinel decreases by ~20 %.

In this paper, we report some recent developments of the diffraction-based absolute X-ray energy calibration method. In this calibration method, high spatial resolution of the measured detector offset is essential. To this end, a remotely controlled long-translation motorized stage was employed instead of the less convenient gauge blocks. It is found that the precision of absolute X-ray energy calibration (ΔE/E) is readily achieved down to the level of 10−4 for high-energy monochromatic X-rays (e.g. 80 keV). Examples of applications to pair distribution function (PDF) measurements and energy monitoring for high-energy X-rays are presented.

The structure of fluid Hg during the metal–non-metal transition has been modelled by Reverse Monte Carlo simulation in terms of the structural factors S ( Q ) measured by X-ray diffraction at SPring-8. The full region of S ( Q ) including S (0) was employed in the simulation so as to take the effect of fluctuation phenomenon into account. The modelling reveals that as the M–NM transition is approached, the distribution of coordination numbers, P ( N ), of the first-neighbor shell broadens obviously and shifts to lower values, supporting the speculation of Franz’s model. Furthermore, the coordination number P S ( N ), denoted for atoms with a shorter bond, changes markedly in width and average value, while much smaller is found for that of longer bond as the density decreases. The variation of P S ( N ) of the atoms with the shorter bond are directly related to the M–NM transition of fluid Hg.

One fascinating high-pressure behavior of tetrahedral glasses and melts is the local coordination change with increasing pressure, which provides a structural basis for understanding numerous anomalies in their high-pressure properties. Because the coordination change is often not retained upon decompression, studies must be conducted in situ . Previous in situ studies have revealed that the short-range order of tetrahedrally structured glasses and melts changes above a threshold pressure and gradually transforms to an octahedral form with further pressure increase. Here, we report a thermal effect associated with the coordination change at given pressures and show distinct thermal behaviors of GeO 2 glass in tetrahedral, octahedral, and their intermediate forms. An unusual thermally induced densification, as large as 16%, was observed on a GeO 2 glass at a pressure of 5.5 gigapascal (GPa), based on in situ density and x-ray diffraction measurements at simultaneously high pressures and high temperatures. The large thermal densification at high pressure was found to be associated with the 4- to 6-fold coordination increase. Experiments at other pressures show that the tetrahedral GeO 2 glass displayed small thermal densification at 3.3 GPa arising from the relaxation of intermediate range structure, whereas the octahedral glass at 12.3 GPa did not display any detectable thermal effects.

X-ray diffraction measurements for expanded fluid mercury have been carried out in a wide density region from the liquid to dense vapour region using synchrotron radiation at SPring-8. We have developed a new high-pressure vessel with seven windows to collect the scattered X-rays for energy-dispersive X-ray diffraction measurements under high temperature and high pressure, and present the new data. It was found that the reliability of the structure factors, S(k), and the accuracy of the pair distribution functions, g(r), are much better. Reliable relations of the coordination number and the correlation distance with the density of fluid Hg were obtained. Structural changes with decreasing density are discussed in relation to the metal–non-metal transition in fluid Hg based on the new results.

X-ray diffraction measurements for expanded fluid selenium have been carried out in a wide density region from the liquid to the dense vapor using synchrotron radiation at SPring-8. We have developed a new high pressure vessel with seven windows to measure scattered X-rays and the reliability of the structure factors becomes much better. The measurements were made in the semiconductor–metal (SC–M) transition region from 600 to 1500 °C near 800 bar. The structure factors in the dense vapor region from 300 to 441 bar at 1650 °C are obtained for the first time. Structural changes in the SC–M transition region and the structure of the dense selenium vapor are discussed, based on these new results.

Energy-dispersive X-ray diffraction measurements using synchrotron radiation at SPring-8 for fluid Se have been carried out at temperatures up to 1650 °C and pressures up to 878 bar, including the dense vapour region, to investigate the structural change in the semiconductor-to-metal (SC–M) transition in expanded fluid Se. We obtained the structure factors, S ( k ), and the pair distribution functions, g ( r ), with a fairly good accuracy. Besides confirming the preservation of twofold-co-ordinated structure, the contraction of nearest co-ordination distance and the existence of asymmetry of the first peak in the g ( r ) in the metallic fluid region, it was found that the line shape of the first peak in the g ( r ) changes as well as the value of the first minimum in the g ( r ) increases obviously with increasing metallic properties. These results indicate that both the existence of different intrachain bonds and the interchain interaction are important for the mechanism of SC–M transition in fluid Se.

The amorphous Sm2Fe15Ga2C2 ribbons were rapidly thermal annealed at various temperatures for various times. From the X-ray diffraction patterns, two phases, i.e. 2 : 17 phase and alpha-Fe, were always found when the ribbons were annealed at temperature above 700 degrees C. The demagnetization curves also verified this two-phase behavior. However, from the TEM studies, only 2: 17 phase was found. This led to the suggestion that the alpha-Fe precipitates were caused by the oxidation of Sm and only took place at the surface of the annealed ribbons. Moreover, from the TEM images, crystallization of 2 : 17 phase was found to begin at about 600 degrees C. The ribbons annealed at 700 or 900 degrees C for 1 min showed well-defined grains in the absence of alpha-Fe. Their grain sizes were measured to be about 100 nm for 700 degrees C x 1 min and 250 nm for 900 degrees C x 1 min, respectively. It was thus suggested that the Sm2Fe15Ga2C2 2 : 17 type structure obtained from the melt-spinning technique remains stable up to at least 900 degrees C. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Rare earth phosphors have been widely studied because of their sharp emission lines and excellent optical performance. However, photoluminescence (PL) tuning by crystal field in Er3+ embedded phosphors has always been a challenge. Here, we demonstrate that pressure can help to enhance the red and green light emission simultaneously in Er:GdVO4. Synchrotron X-ray diffraction investigations revealed that a structural phase transition was responsible for the enhancement. Our work brightens the future prospects for applications of Er3+-based PL materials in various fields, such as high power lasers and (bio) medical imaging.

Density-driven polyamorphism of $\mathrm{Ge}{\mathrm{O}}_{2}$ glass under high pressure has been studied by density, x-ray scattering, and optical Raman measurements. Density data obtained by an x-ray absorption method display distinct compression behavior in different pressure regions, with rapid density increases at 5 and $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and a plateau at $6--9\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Simultaneous x-ray diffraction reveals that the position of the first sharp diffraction peak (FSDP) increases nearly linearly towards higher scattering vector with pressure up to $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Both the width of the FSDP and the Raman stretching band of Ge-O-Ge $(419\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})$ increase with pressure but exhibit changes in behavior at 2.5 and $7.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, indicating intermediate states exist in the glass before the collapse of local tetrahedral and pentahedral structural units, respectively. At pressures above $15\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, post-octahedral compression with progressive enhancement in network correlation is observed. The results indicate not only the discrete but also rotating intermediate states exist in $\mathrm{Ge}{\mathrm{O}}_{2}$ glass under pressures up to $35\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.

In this paper, we report a method of precise and fast absolute x-ray energy calibration over a wide energy range using an iterative x-ray diffraction based method. Although accurate x-ray energy calibration is indispensable for x-ray energy-sensitive scattering and diffraction experiments, there is still a lack of effective methods to precisely calibrate energy over a wide range, especially when normal transmission monitoring is not an option and complicated micro-focusing optics are fixed in place. It is found that by using an iterative algorithm the x-ray energy is only tied to the relative offset of sample-to-detector distance, which can be readily varied with high precision of the order of 10(-5) -10(-6) spatial resolution using gauge blocks. Even starting with arbitrary initial values of 0.1 Å, 0.3 Å, and 0.4 Å, the iteration process converges to a value within 3.5 eV for 31.122 keV x-rays after three iterations. Different common diffraction standards CeO(2), Au, and Si show an energy deviation of 14 eV. As an application, the proposed method has been applied to determine the energy-sensitive first sharp diffraction peak of network forming GeO(2) glass at high pressure, exhibiting a distinct behavior in the pressure range of 2-4 GPa. Another application presented is pair distribution function measurement using calibrated high-energy x-rays at 82.273 keV. Unlike the traditional x-ray absorption-based calibration method, the proposed approach does not rely on any edges of specific elements, and is applicable to the hard x-ray region where no appropriate absorption edge is available.

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes noticeable at high pressures above 10 GPa, which can be monitored with a precision better than 1%, as demonstrated by measurements on crystalline Ag. We have applied the developed method to measure densities of the classic network-forming GeO(2) glass in octahedral form at pressures up to 56 GPa. The fit to the pressure-volume data with the Birch-Murnaghan equation from 13 to 56 GPa gives parameters of V(0)=23.2+/-0.4 cm(3)mol and K=35.8+/-3.0 GPa, assuming that K(')=4. This method could be applicable for in situ determination of the density of liquids and other noncrystalline materials using a diamond anvil cell up to ultrahigh pressures.