金红石高温高压相变的Raman光谱特征

以Ar作压力介质,在准静水压力条件下,利用激光加热DAC技术和显微Raman光谱原位测试技术,在0～35 GPa压力范围开展金红石的高温高压相变研究。在室温条件下,金红石结构TiO₂于13.4 GPa开始转变成斜锆石相,于21 GPa时转变完全,并直到35 GPa时斜锆石相稳定存在。在压力分别为29.4和35.0 GPa时,用YAG激光器发出的波长为1.064 μm的红外激光束扫描加热样品,TiO₂斜锆石高压相转变成另一Pbca结构高压相。卸压时,Pbca相于26.3 GPa时转变成斜锆石相。斜锆石相转变成Pbca相需要加热才能发生,而卸压时却在较小的压力区间即迅速转变完全,两相转变压力边界在28 GPa左右。进一步卸压,斜锆石相直到11 GPa仍稳定,在7.6 GPa时斜锆石相与α-PbO2相两相共存,5 GPa时完全转变成α-PbO₂相,并直到常压该相以亚稳定态存在。     

高压下天然顽火辉石能量色散X射线粉末衍射研究

 在北京同步辐射装置（BSRF）高压站对采自于河北大麻坪的天然顽火辉石,在室温高压（0~31.64 GPa）下,利用金刚石压腔装置（DAC）,进行了能量色散X射线粉末衍射（EDXD）原位测量,得到了顽火辉石在不同压力下的衍射图谱,并利用UnitCell软件进行解谱,获得了其晶胞参数a、b、c和晶胞体积V及其随压力的变化,最后利用Murnaghan等温方程得到了天然顽火辉石的体积模量K_T(0)=172 GPa、压缩系数及p-V状态方程,发现沿a、b、c三方向的压缩系数存在明显的各向异性,结果与斜方辉石的弹性波速各向异性完全一致。     

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。     

Study of high pressure structural stability of CeO2 nanoparticles

In situ high pressure XRD diffraction and Raman spectroscopy have been performed on 12 nm CeO₂ nanoparticles. Surprisingly, under quasihydrostatic conditions, 12 nm CeO₂ nanoparticles maintain the fluorite-type structure in the whole pressure range (0-51 GPa) during the experiments, much more stable than the bulk counterpart (P_T～31 GPa). In contrast, they experienced phase transition at pressure as low as 26 GPa under non-hydrostatic conditions (adopting CsCl as pressure medium). Additionally, 32-36 nm CeO₂ nanoparticles exhibit an onset pressure of phase transition at 35 GPa under quasihydrostatic conditions, and this onset pressure is much lower than our result. Further analysis shows both the experimental condition (i.e., quasihydrostatic or non-hydrostatic) and grain size effect have a significant impact on the high pressure behaviors of CeO₂ nanomaterials.     

Phase transitions in a hydrogen-rich compound：tetramethylsilane

High-pressure behavior of tetramethylsilane is investigated by synchrotron powder X-ray diffraction and Raman scattering at pressures up to 30 GPa and room temperature. Our results reveal the analogous phase transitions, though slight hysteresis for the certain phases. A new phase is found to appear at 4.2 GPa due to the disappeared Raman mode. These findings offer the possibility to understand the evolution of the H-H bonding with pressure in such hydrogen-rich compounds.     

In-Situ Conductivity Measurement of BaF2 under High Pressure and High Temperature

We perform the in-situ conductivity measurement on BaF2 at high pressure using a microcircuit fabricated on a diamond anvil cell. The results show that BaF2 initially exhibits the electrical property of an insulator at pressure below 25 GPa, it transforms to a wide energy gap semiconductor at pressure from 25 to 30 GPa, and the conductivity increases gradually with increasing pressure from 30 GPa. However, the metallization predicted by theoretical calculation at 30-33 GPa cannot be observed. In addition, we measure the temperature dependence of the conductivity at several pressures and obtain the relationship between the energy gap and pressure. Based on the experimental data, it is predicted that BaF2 would transform to a metal at about 87 GPa and ambient temperature. The conductivity of BaF2 reaches the order of 10^-3Ω^-1 cm^-1 at 37 GPa and 2400 K, the superionic conduction is not observed during the experiments, indicating the application of pressure elevates greatly the transition temperature of the superionic conduction.     

高压下纳米尺寸Sr2FeMoO6粉末的结构稳定性和电学特性的研究

 采用高分子网络凝胶法，通过控制其化学反应过程，合成了高纯的多晶纳米级粉末Sr₂FeMoO₆样品A（50 nm）和样品B（100 nm）。对其在高压下的结构稳定性和电学性质进行了研究，并将样品A和样品B的实验结果与已报道的粒度达微米级的块状Sr₂FeMoO₆样品C的实验结果进行了对比。在实验测量范围内，样品A（50 nm）呈现出最大的体弹模量B₀，并在电阻-压力曲线中，电阻下降区域表现出相对较缓的变化率，晶界效应可以用来很好地解释此结果。电学性质测量实验表明，样品在高压下发生了电子结构相变。     

Compressibility of Lattice Parameters of Several Layered Compounds

The lattice parameters of AlB2, MgB2 and TiB2 under pressures are determined with a high-energy synchrotron source in a diamond anvil cell. The experimental results indicate that these three compounds have different mechanical behaviour under pressures, TiB2 is the hardest and MgB2 is the softest among the three materials. The phenomena are explained in terms of bonding strength in the crystal. Our results may be helpful for understating the decrease of the superconducting transition temperature of MgB2 under pressures.     

钨酸锆制备与高压下的相变研究

采用固相烧结法制备了纯度较高的钨酸锆(ZrW2O8)粉体,并利用金刚石对顶压砧(DAC)对其进行了原位高压同步辐射X射线衍射研究。结果表明:在常温下,压力0.27GPa附近,晶体的对称性降低,并发生α-ZrW2O8向γ-ZrW2O8晶体结构相变;压力3.81GPa附近,γ-ZrW2O8完全转变为非晶相。通过拟合得到α-ZrW2O8的体弹模量B=(40.0±3.8)GPa,γ-ZrW2O8的体弹模量B=(37.0±3.0)GPa。     

FeSi2单晶化学气相生长

利用化学气相输运方法, 以碘作为传输剂, 在封闭的石英安瓿中制备出了优质新型的光电及热电半导体材料β-FeSi₂单晶. 在大量实验基础上深入研究了生长工艺对单晶质量、形态的影响, 除了得到大尺寸针状β-FeSi₂单晶外, 还获得了大尺寸颗粒状单晶. 通过改变衬底温度, 得到了四面体柱状优质的α-FeSi₂单晶.