纳米晶钛酸铅镧体系的软模及铁电相变研究

采用Raman散射方法系统研究了Pb_1-xLa_xTiO₃(PLT)的软模行为和铁电相变.结果表明,随着晶粒尺寸的减小,Pb_0.86La_0.14TiO₃(PLT14)能从常温常压下的四方铁电相转化为立方顺电相;在高温常压及常温高压下纳米晶PLT14的相变温度和压力均比体材料情况下低;对于不同晶粒尺寸的PLT体系,系统从四方相转化为立方相的相边界随晶粒尺寸的减小移向更低的La离子浓度,还论述了软模随晶粒尺寸、温度、压力和La离子浓度的变化行为以及系统发生相变的机制.     

Effects of high pressure on the Raman and fluorescence emission spectra of two novel 1,3,4-oxadiazole derivatives

The effects of pressure on the fluorescence emission and Raman spectra of 1,4-bis[（4-methyloxyphenyl）-1,3,4-oxadiazolyl]- 2,5-bisheptyloxyphenylene （OXD-2） and on the fluorescence emission spectra of 1,4-bis[（4-methylphenyl）- 1,3,4-oxadiazolyl]phenylene （OXD-1） are investigated using a diamond anvil cell. With the increase of pressure, the intensity of the fluorescence emission increases and reaches maxima at 13GPa for OXD-1 and at 9.6GPa for OXD-2. The effect of pressure on the peak position of the emission shows a similar trend, red shift with the increase of pressure. But at higher pressures, the intensity of emission drops down dramatically. The Raman spectra of OXD-2 indicate that there appears a structural change at ca 3GPa.     

分子晶体的高压Raman光谱及结构相变

 本文综合我们从NH₃F（氟化胺）、HCCl₃（氯仿）、HCBr₃（溴仿）、S₈（硫）和C₃N₆H₆（三聚氰胺）等分子晶体获得的高压Raman光谱数据，讨论了分子晶体Raman光谱的谱带强度，频率位移，晶场劈裂和Grüneisen常数等对压力的依赖关系。总结了分子晶体压致结构相变的光谱证据和高压新相结构确定的几种方法。     

PbTe的高温高压合成

 以高温高压为手段，在4～5GPa压力和700～1 200 K温度条件下，成功地合成出了PbTe。对合成样品进行了X射线测试分析，结果表明，合成的PbTe样品是具有NaCl结构的多晶，而PbTe的取向随着合成压力的升高发生变化。扫描电镜分析结果显示：高压合成的PbTe样品，其晶粒有了明显的取向；电阻率比常压样品低1～2个数量级，并随合成压力的升高而降低；热导率也同时低于常压合成的PbTe样品。以上结果说明，高压合成方法是改善材料性能的重要手段。     

Effects of High Pressure on BC3

High-pressure phases of BC3 are studied within the local density approximation under the density functional theory framework. When the pressure reaches 20 GPa, the layered BC3 that is a semiconductor at ambient pressure, becomes metallic. As the pressure increases, the material changes into a network structure at about 35 GPa. To understand the mechanism of phase transitions, band structure and density of states are discussed. With the increase of pressure, the width of bands broadens and the dispersion of bands enlarges. Additionally, the density of states of the network bears great resemblance to that of diamond. Formation of the sp3 bonding in the network is the main reason for the structural transformation at 35 GPa.     

石墨C—C键的温度、压力效应及键长的Raman频率表征

本文在20℃～550℃,0GPa～13GPa压力区间内测量了石墨的Raman光谱,并在20℃～1100℃温度范围内做了石墨的X光衍射实验。实验结果表明,TG64型石墨在20℃～750℃温度范围内C-C键长随温度升高而收缩,温度高于750℃时键长随温度升高而膨胀。高压Raman的结果表明,石墨的E_(2q)活性模的频率随压力升高分段线性收缩,分段点在4GPa附近。同时还对在常温常压下利用Raman频率计算石墨C—C键长的Fitzer公式做了修正,并分别给出了温度和压力的修正因子以及C—C键力常数随温度、压力变化的规律。     

高温对富勒碳的影响

 对富勒碳的高温性质进行了研究。实验发现在高于870 K时，富勒碳分子结构被破坏，变成了碳原子的无定形态。讨论了富勒碳所处空间性质对其热性质的影响，认为富勒碳分子的碰撞产生的极化是富勒碳分子结构破坏的主要原因。     

Phase Transition Behavior of LiCr 0.35 Mn0.65O2 under High Pressure by Electrical Conductivity Measurement

The electrical conductivity of powdered LiCr 0.35 Mn0.65O2 is measured under high pressure up to 26.22 GPa in the temperature range 300-413 K by using a diamond anvil cell. It is found that both conductivity and activation enthalpy change discontinuously at 5.36 GPa and 21.66 GPa. In the pressure range 1.10-5.36 GPa, pressure increases the activation enthalpy and reduces the carrier scattering, which finally leads to the conductivity increase. In the pressure ranges 6.32-21.66 GPa and 22.60-26.22 GPa, the activation enthalpy decreases with pressure increasing, which has a positive contribution to electrical conductivity increase. Two pressure-induced structural phase transitions are found by in-situ x-ray diffraction under high pressure, which results in the discontinuous changes of conductivity and activation enthalpy.     

人造金刚石与硬质合金复合材料的研制

 本实验选用TiH₂及其它微量元素做粘结剂，在DS-029B型六面顶压机上烧结人造金刚石与硬质合金复合材料。实验中，采取TiH₂脱氢与金刚石净化同时进行的工艺，在高真空和一定温度下脱氢，得到高活性的新鲜钛，使其具有更强的粘结作用，以获得高磨耗比的金刚石复合材料。实验中比较了不同净化温度对磨耗比的影响；同一种粘结剂不同含量与磨耗比之间的关系；同时还测试了其耐热性及时间极限。结果表明，这种复合材料在850 ℃下，加热3 min，磨耗比没有明显改变。