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Phase transition of solid-state materials is a fundamental research topic in condensed matter physics, materials science and geophysics. It has been well accepted and widely proven that isostructural compounds containing different cations undergo same pressure-induced phase transitions but at progressively lower pressures as the cation radii increases. However, we discovered that this conventional law reverses in the structural transitions in 122-type iron-based superconductors. In this report, a combined low temperature and high pressure X-ray diffraction (XRD) measurement has identified the phase transition curves among the tetragonal (T), orthorhombic (O) and the collapsed-tetragonal (cT) phases in the structural phase diagram of the iron-based superconductor AFe2As2 (A=Ca, Sr, Eu, and Ba). The cation radii dependence of the phase transition pressure (T R cT) shows an opposite trend in which the compounds with larger ambient radii cations have a higher transition pressure. [ABSTRACT FROM AUTHOR] more...

The volume change of liquid and solid gallium has been studied as a function of pressure and temperature up to 3.02GPa at 300K and up to 3.63GPa at 330K using synchrotron x-ray microtomography combined with energy dispersive x-ray diffraction techniques. Two sets of directly measured P-V data at 300K and 330K were obtained from 3D tomography reconstruction data, and the corresponding isothermal bulk moduli were determined as 23.6 (0.5) GPa and 24.6 (0.4) GPa, respectively. The existence of a liquid-liquid phase transition region is proposed based on the abnormal compressibility of Ga melt at about 2.44GPa and 330K conditions. [ABSTRACT FROM AUTHOR] more...

A comparative study of the equation of states of hydrous (0.4 wt% H2O) and anhydrous San Carlos olivine (<30 ppm H2O) was conducted using synchrotron X-rays up to 11 GPa in a diamond anvil cell (DAC) at ambient temperature. Both samples were loaded in the same high-pressure chamber of the DAC to eliminate the possible pressure difference in different experiments. The obtained compression data were fitted to the third-order Birch-Murnaghan equation of state, yielding a bulk modulus K0 = 123(3) GPa for hydrous olivine and K0 = 130(4) GPa for anhydrous olivine as K0' fixed at 4.6. Therefore, 0.4 wt% H2O in olivine results in a 5% reduction in bulk modulus. Previous studies reported bulk modulus reduction by water in olivine's high-pressure polymorph (wadsleyite), to which the transformation from olivine gives rise to the seismic discontinuity at 410 km depth. The new data results in a reduction in the magnitude of the discontinuity by 50% in vP and 30% in vS (for 1:5 water partitioning between olivine and wadsleyite) with respect to anhydrous mantle. Previous knowledge of the influence of water on this phase transition has been in opposition to a large amount of water [e.g., 200 ppm by Wood (1995)] existing at 410 km depth. Calculation of the seismic velocities based on newly available elasticity data of the hydrous phases indicates that the presence of water is favorable for the mineral composition model (pyrolite) and seismic observations in terms of the magnitude of the 410 km discontinuity. [ABSTRACT FROM AUTHOR] more...

The crystal structure of NaMgF3 perovskite (neighborite) has been studied at 4 GPa and temperatures up to 1000 °C using the Rietveld structure-refinement method. In situ synchrotron X-ray powder diffraction data was collected using monochromatic radiation. The orthorhombic (Pbnm) to cubic (Pm3̅m) transition was observed when the temperature increased from 900 to 1000 °C. Structure refinements show that the ratio of polyhedral volumes of the A and B sites (VA/VB) of the orthorhombic phase increases with temperature, approaching the ideal value (5) for the cubic structure. However, this ratio becomes smaller at 4 GPa compared to the result from previous studies at the same temperature but ambient pressure, indicating that pressure makes it more difficult to transform from the orthorhombic phase to the cubic phase in this kind of perovskite. [ABSTRACT FROM AUTHOR] more...

A zone-axis synchrotron diffraction study of complex and inhomogeneous Fe1-xO thin single crystal under pressure is presented in this letter. Using this method, four phases are observed to coexist in a single crystal of Fe1-xO at 35 GPa in diamond-anvil cells. One phase has cubic symmetry, whereas the other three phases have not been reported previously and can be interpreted as either orthorhombic or monoclinic. The discovery of multiple phases existing in Fe1-xO indicates that structural inhomogeneity of the sample can be induced under high pressure, a result that has important implications for the high P-T behavior of this complex material. Such information is not available using conventional diffraction techniques. [ABSTRACT FROM AUTHOR] more...

The article discusses various reports published within the issue, including one on the "Development of Cutting-Edge High-Pressure Programs at Non-Dedicated Beamlines," one on the "Further Development and Integration at Dedicated High-Pressure Beamlines," and one on the "Novel Techniques for High-Pressure Research." more...

Background The free training for rural order-oriented medical students has trained a large number of primary health personnel for the central and western regions of China. By the summer of 2021, the first order-oriented medical graduates had completed their compulsory service and face the choice of staying or leaving. The income is an important influencing factor of their choices, however, there are still few studies on the income of order-oriented medical graduates. Objective The panel data of order-oriented medical graduate cohort study was used to compare and analyze the change trend of the income of order-oriented medical graduates and general clinical graduates in the early career, and to explore the influencing factors of the change of income. Methods Qinghai University, Guangxi Medical University, Jiujiang Medical University and Gannan Medical University were selected to establish the order-oriented medical graduate cohort every year from 2015 to 2019, matching the general clinical graduates of the same grade as controls. The baseline survey was conducted, including basic information and family information. A total of four follow-up surveys were conducted in 2016, 2017, 2018 and 2020, including the status of standardized resident training (hereinafter referred to as "standardized training") , passing of medical licensing examination, working conditions and other information. Fixed effects model was used to explore the factors influencing the income of order-oriented medical graduates and general clinical graduates, and propensity score matching (PSM) was used to test the stability of the results. Results In the first two years after graduation, the income of order-oriented medical graduates was higher than general clinical graduates, and the difference was statistically significant (P more...

In the present study, we summarize indications for the existence of kinked post-perovskite structures in the MAS system. X-ray diffraction data and Raman spectra of aluminous magnesium metasilicate post-perovskite are inconsistent with the CaIrO3 structure. Instead the observations are consistent with structures intermediate between the perovskite and the CaIrO3 structure. Ab initio calculations show that the enthalpies of the kinked structures are slightly higher than the CaIrO3 structure at 0 K. Finite temperature, minor element chemistry, kinetics of phase transformation, and actual stress regime are plausible reasons for the observed differences between the present and the previously reported post-perovskite phases. [ABSTRACT FROM AUTHOR] more...

Neighborite (NaMgF3) with the perovskite structure, transforms to a post-perovskite (ppv) phase between 27 and 30 GPa. The ppv phase is observed to the highest pressures achieved (56 GPa) at room temperature and transforms to an as yet unknown phase upon heating. Rietveld structure refinement using monochromatic synchrotron X-ray diffraction data provide models for the perovskite and post-perovskite structures at high pressure. The refined models at 27(1) GPa indicate some inter-octahedral F-F distances rival the average intra-octahedral distance, which may cause instability in the perovskite structure and drive the transformation to the post-perovskite phase. The ratio of A-site to B-site volume (VA/VB) in perovskite structured NaMgF3 (ABX3), spans from 5 in the zero-pressure high-temperature cubic perovskite phase to 4 in this high-pressure perovskite phase at 27(1) GPa, matching the VA/VB value in post-perovskite NaMgF3. Using Rietveld refinement on post-perovskite structure models, we observe discrepancies in pattern fitting, which may be described in terms of development of sample texture in the diamond-anvil cell, recrystallization, or a change of space group to Cmc21, a non-isomorphic subgroup of Cmcm--the space group describing the structure of CaIrO3. [ABSTRACT FROM AUTHOR] more...

The article reports on the structure stability and compressibility of iron-based superconductor Nd(O0.88F0.12)FeAs under high pressure. It discusses research on La(O1-xFxFeAs (x=0.05-0.12) and the use of Nd(O0.88F0.12)FeAs to examine properties under high pressure. An experiment using a diamond anvil cell technique with an angle-dispersive synchroton X-ray diffraction technique resulted in pressure-induced structural transition. more...