Compression Behaviour and Equation of State of Zr44.4Nb7Cu13.5Ni10.9Be24.3 Bulk Metallic Glass up to 39 GPa

The compression of Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glass (BMG) is investigated at room temperature up to 39 GPa using in situ high-pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state of the BMG is obtained by the calculation of the radial distribution function. Pressureinduced structural relaxation is exhibited. It is found that below about 6 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise to rapid volumetric change, and the structural relaxation results in structural stiffness under higher pressure.     

Compression behavior and phase transition of β-Si_3N_4 under high pressure

The compressibility and pressure-induced phase transition of β-Si_3N_4 were investigated by using an angle dispersive x-ray diffraction technique in a diamond anvil cell at room temperature. Rietveld refinements of the x-ray powder diffraction data verified that the hexagonal structure(with space group P63/m, Z = 2 formulas per unit cell) β-Si_3N_4 remained stable under high pressure up to 37 GPa. Upon increasing pressure, β-Si3 N4 transformed to δ-Si_3N_4 at about 41 GPa. The initial β-Si_3N_4 was recovered as the pressure was released to ambient pressure, implying that the observed pressureinduced phase transformation was reversible. The pressure–volume data of β-Si_3N_4 was fitted by the third-order Birch–Murnaghan equation of state, which yielded a bulk modulus K_0= 273(2) GPa with its pressure derivative K_0= 4(fixed)and K0= 278(2) GPa with K 0= 5. Furthermore, the compressibility of the unit cell axes(a and c-axes) for the β-Si_3N_4 demonstrated an anisotropic property with increasing pressure.     

Phase Transition of FeS in Terms of In-Situ Resistance Measurement

Electrical properties of stoichiometric iron sulfide （FeS） are investigated under high pressure with a designed diamond anvil cell. The process of phase transition is reflected by changing the electrical conductivity under high pressure, and the conductivity of FeS with the NiAs structure is found to be much smaller than other phases. Two new phase transitions without structural change are observed at 34.7 GPa and 61.3 GPa. The temperature dependence of the conductivity is found to be similar to that of a semiconductor when the pressure is higher than 35 GPa     

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.     

绿柱石的原位高压X射线研究

 采用同步辐射光源和金刚石对顶砧（DAC）技术,对绿柱石进行了室温下的原位高压能散X射线衍射（EDXD）研究,实验的最高压力为19.2 GPa。在实验压力范围内,未观察到绿柱石发生相变,轴压缩率c大于a;在小于9.3 GPa的压力范围内,其体积压缩率符合二阶Murnaghan状态方程,而压力在9.3～19.2 GPa范围内时,其体积压缩率有所增加,且体积-压力关系近乎线性变化。     

非晶态SiO2的高温高压转变研究

利用金刚石对顶砧高压装置和激光双面加热技术, 以经700°C热处理后的吉林长白山硅藻土作为非晶态SiO₂样品,在0—4GPa, 1000—1300K温压条件下开展同步辐射X射线衍射原位测试(EDXD方法), 研究非晶态SiO₂在高温高压条件下的结晶转变方式. 测试结果表明, 在0.8—2.4GPa, 1000—1300K温压条件下, 非晶态SiO₂转变成α-石英而非β-石英或方石英, 其结晶温度较常压下非晶态SiO₂晶化所需温度明显较低, 表明压力有利于降低非晶态SiO₂转变的活化能, 并与常压下的结晶产物不同. 在3—4GPa, 1300K温压条件下, 非晶态SiO₂和石英均转变成了柯石英.     

二联吡啶及其二氮取代衍生物电子性质和非线性光学性质的理论研究

采用量子化学PM3方法优化得到二联吡啶及四种二氮取代衍生物的稳定结构,利用ZINDO-SOS∥PM3方法对它们的二阶和三阶非线性光学性质进行计算.结果表明,该类化合物具有良好的非线性光学性质,其中1,6,1′,6′-四氮取代联苯的β值最大,为73 2082C·m,而2,4,2′,4′-四氮取代联苯的三阶非线性光学性质最显著.     

高压衍射光路的准直与散射背底屏蔽

在同步辐射高压X射线光路中,通过建立准直系统屏蔽来自金刚石的康普顿散射和实验环境中的杂散光,有效地降低了散射背底.通过两次专用光期间的测试表明,准直系统对于信噪比的提高有较为显著的效果,使以前不能进行有效测量的一些高压样品可以得到较好的能量色散X射线衍射数据,并为进行MPa压力下的原位测试提供了有效的手段.     

ZnS:Eu纳米晶的高压相变研究

采用同步辐射能量色散X射线衍射技术和金刚石对顶砧高压装置,对ZnS:Eu纳米晶进行了原位高压X光衍射实验.最高压力为30.8Pa.当压力为11.5GPa时,ZnS:Eu发生了一次从纤锌矿到闪锌矿的结构相变.在压力为16.0GPa时,又发生了明显的结构相变,相变后的结构为岩盐矿,其相变压力较体材料高.得到了Birch-Murnaghan状态方程、ZnS:Eu纳米晶的体模量和压力导数.ZnS:Eu纳米晶的体模量高于体材料的值,表明纳米材料较体材料的硬度高.     

α-LiIO3的高压同步辐射研究

通过原位下的高压同步辐射X光衍射技术,对具有六方结构的α-LiIO₃的相稳定性进行了研究,压力范围从0.1MPa到36.0GPa.实验表明在15.6GPa—23.8GPa压力区间,α-LiIO₃发生了结构相变.