Structural Stability of CaCuMn6O12 under High Pressure and Low Temperature

In situ high pressure energy-dispersive x-ray synchrotron radiation diffraction and resistance experiments are carried out on CaCuMn6O12. Its crystal structure is stable in the measured pressure range. The equation of state of CaCuMn6O12 is obtained from the V/Vo - P relationship （V and Vo are the volumes at pressure P and at atmosphere）. The bulk modulus Bo is calculated based on the Birch-Murnaghan equation. Low temperature x-ray diffraction shows no phase transition occurring down to 160K.     

高压下ZnSe 纳米带的结构相变及拉曼散射研究

 利用高压原位角散X射线衍射实验研究了ZnSe纳米带的结构稳定性。发现样品在12.6 GPa 附近存在一个从立方闪锌矿型到立方岩盐矿型的结构相变,并且在相变点附近存在较大的体积收缩,相对体积变化率达13%。利用Birch-Murnaghan 状态方程拟合,得到了闪锌矿相的体弹模量约为56 GPa,略低于体材料的体弹模量（约67 GPa）;并得到其立方岩盐矿相的体弹模量约为116 GPa。高压拉曼散射实验结果表明,横光学声子模散射峰在5.5 GPa压力附近发生劈裂,纵光学声子模散射峰在12.8 GPa压力以上逐渐消失。根据角散实验的体弹模量数据,计算得到了闪锌矿相中对应不同声子模式的格林爱森常数。     

Pressure-Induced Phase Transition in BaTiO3 Nanocrystals

The crystal structure and electric properties of BaTiO3 nanocrystals are studied by in situ high-pressure synchrotron radiation x-ray powder diffraction. The phase transition takes place not only in the samples of BaTiO3 nanocrystals that are tetragonal phase with grain sizes more than 100nm, but also in the samples of BaTiO3 nanocrystals that are cubic phase with grain sizes less than 100nm. The pressures of phase transition are found to increase with decrease of the grain size from about 4 to 10GPa for crystallites ranging from 200 to 10nm in radius. The bulk moduli are calculated according to Birch-Murnaghan state equation before and after the phase transition.     

Isostructural Phase Transition of TiN under High Pressure

In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaCltype structure have been conducted with the pressure up to 30.1 GPa by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The experimental results suggest that an isostructural phase transition might exist at about 7 GPa as revealed by the discontinuity of V/Vo with pressure.     

Zn2SnO4纳米线高压下的相变研究

 利用金刚石对顶压砧（DAC）对具有反尖晶石结构的透明导体氧化物Zn₂SnO₄（ZTO）纳米线进行了原位高压同步辐射角散X射线衍射（ADXRD）研究。结果发现：在压力为12.9 GPa附近,晶体的对称性降低,并发生晶体结构相变,产生中间过渡相;当压力为32.7 GPa时,发生高压相变,形成高压相。在样品加压前后,纳米线的形貌发生了很大的变化。通过Birch-Murnaghan方程,拟合得到B′₀=4时的体弹模量B₀ =(168.6±9.7) GPa。     

Hydrostaticity of Pressure Media in Diamond Anvil Cells

Hydrostaticity under high pressure of several materials from solid, fluid to gas, which are widely used as pressure media in modern high-pressure experiments, is investigated in diamond anvil ceils. Judging from the R-line widths and R1 - R2 peak separation of Ruby fluorescence, the inert argon gas is hydrostatic up to about 30 GPa. The behavior of silicon oil is found to be similar to argon at pressures less than 10 GPa, while the widening of R-lines and increase of R1 - R2 peak separation at higher pressure loads indicate a significant degradation of hydrostaticity. Therefore silicon oil is considered as a good pressure medium at pressures less than 10 GPa but poor at higher pressures.