聚四氟乙烯动态特性的实验研究

 在10~55 GPa的高压范围用化爆装置、采用阻抗匹配法测得了聚四氟乙烯（初始密度ρ₀=2.19 g/cm³）的冲击波速度D和波后粒子速度u之关系为：D=2.10+1.62u（mm/μs）。在0.2~3 GPa的低压范围用气炮装置、采用电磁速度计测量了材料内加、卸载过程的拉格朗日粒子速度波形，获得的冲击加载D-u关系为：D=1.24+3.72u-1.94u²（mm/μs）。实测卸载曲线和加载冲击绝热线接近一致，残余应变似乎不存在或者说很小；弹性区段很不明显，聚四氟乙烯本质上呈现出塑性性质。     

加压对110 K Bi-Pb-Sr-Ca-Cu-O单相样品超导电性的影响

 在静压0~1 GPa（10 kbar）范围内，80~300 K温区，用测量电阻的方法，研究了Bi-Pb-Sr-Ca-Cu-O（起始转变温度T_c^on=110 K，终止转变温度T_c^fi=106 K）的起导电性。观察到超导临界温度T_c随压力以dT_c/dp=2K/GPa的速率增高，而在不同压力下的斜率d logR/dp却保持不变。     

高压下碳化钨压砧走时的测量

 在常温、实验压力为0～3 GPa条件下,利用脉冲反射法测量了纵波在碳化钨压钻中的走时,结果发现,随实验压力升高,碳化钨压砧的走时线性减少。碳化钨压砧被压缩是引起碳化钨压砧的走时减少的主要原因。实验压力（p/GPa）与碳化钨压砧走时减少量（Δt/μs）之间的关系为：Δt=(0.022 33±0.000 81)p。运用这个关系式可以对所测量的岩石弹性波速度进行校正,以获得更为精确的岩石弹性波速度。     

钨合金的超声测量及力学参量估算

 利用两面顶压机和六面顶压机作为压力装置，分别对93钨合金材料进行了高压超声测量。测得了93钨合金材料在常态下的横、纵波声速及在0~3 GPa压力范围内的纵波声速随压力的变化关系。测量结果为：在常温常压下，93钨合金的纵波声速为c_L＝5.135 km/s，横波声速为c_t＝2.987 km/s。纵波声速随压力变化的关系式为：c_L＝5.053+0.602p（GPa）。估算的93钨合金相关力学参量为：G＝157.4 GPa，E＝393.0 GPa，K＝260.2 GPa，λ＝155.3 GPa，μ＝157.4 GPa，ν＝0.248。经过对两种超声测量方法测量结果的比较及冲击波测量数据的验证，这些参数是可靠的。     

超高压下CsBr的结构与相变

 采用金刚石对顶压砧高压装置（DAC）、同步辐射X光源和能散法，对CsBr粉末样品进行了原位高压X光衍射实验，最高压力达115 GPa。观测到在53 GPa左右压力下，CsBr的最强衍射峰(110)劈裂成两个峰，标志了简单立方结构向四方结构的转变；在0至最高压力范围内（相应于V/V₀为1至0.463）测量了晶轴比c/a；在115 GPa内未观测到样品的金属化现象。     

过渡金属锇在高压下的力学特性

 基于密度泛函理论平面波赝势法的第一性原理计算,研究了过渡金属锇在高压下的状态方程、弹性常数和其它力学性质。 计算结果表明：过渡金属锇具有很高的体积模量B₀（423.9 GPa）和弹性常数C₁₁（771.3 GPa）与C₃₃（852.0 GPa）,与金刚石的（B₀=452.8 GPa,C₁₁=C₃₃=1 082.9 GPa）比较,具有超低压缩特性;表征材料抵抗剪切变形能力的弹性常数C₄₄（269.8 GPa）和切变模量（276.8 GPa）只有金刚石的（C₄₄=586.9 GPa,G=537.5 GPa）一半,而所成的又是纯金属键,因此锇不具有超硬性。最后,定性分析了它的高体积模量和低硬度的微观电子机制,这对于设计与合成新的超硬性材料具有启发意义。     

50 GPa下NiO等温状态方程的高压X光研究

 本文采用在位的（in situ）高压X光衍射方法研究了近50 GPa和室温下三方结构NiO的等温压缩行为，并用Murnaghan状态方程对实验值进行了最小二乘法拟合，得到的NiO室温状态方程的相应参量分别为：B₀=223 GPa，B₀'=4.21。在室温压力范围内没有观察到第一类结构相变。NiO在六方指标下的轴比c/a随压力的变化在实验压力范围内可用c/a=2.450~1.569×10^-3（GPa）近似描述。     

Phase Transition and EOS of Cinnabar （α-HgS） at High Pressure and High Temperature

Phase relations and equation of state （EOS） of natural cinnabar （α-HgS） are investigated by high-pressure and high-temperature synchrotron x-ray powder diffraction. The unambiguous cinnabar-rocksalt structure phase boundaries are determined to be PI （GPa）=15.54- 0.014T（℃） and Pupper（GPa）= 23.84- 0.014T（℃） at 300-623K. With K1 fixed at 4, we obtain K0 = 37（4） GPa, （aK/aT）p= -0.025（2） GPaK-1, and α0 = 3.79（20） × 10-5 K-1 for the cinnabar phase of α-HgS. The （aK/aT）p and α0 of cinnabar phase are obtained for the first time. A nearly isotropic compression of cinnabar phase is observed by linear regressions.     

压致硼酸盐晶态物质的非晶化现象研究

 本文用X射线衍射、Eu²⁺的发射谱与激发谱、拉曼谱以及扫描电镜（SEM）颗粒形貌，研究了常压下合成的具有正交结构的SrB₂O₄:Eu²⁺晶体在3.0~7.0 GPa压力下的晶态非晶化现象。分析结果表明，压力导致晶粒细化和晶态非晶化。晶粒尺寸由常压下的微米量级细化为几十个纳米量级，随压力的变化为：2 μm（0.1 MPa），49.4 nm（3.0 GPa），29.7 nm（5.0 GPa），25.1 nm（7.0 GPa）。晶态与非晶态体积比随压力增加而减小，分别为：70/30（3.0 GPa），63/37（5.0 GPa），57/43（7.0 GPa）。在压力下Eu²⁺是处在晶态与非晶态两种不同的低对称的环境中。纳米级晶粒是以亚晶粒形式存在于微米级大晶粒中的，压致非晶态可能组成了纳米亚晶粒的界面区。     

碳水混合物冲击压缩特性的理论研究

 采用固-液双相混合模型和分子流体的微扰变分统计理论,分别计算了石墨-水体系（ρ₀=1.233 g/cm³）和金刚石-水体系（ρ₀=1.238 g/cm³）的冲击压缩特性。结果表明：（1）在不发生石墨→金刚石相变和化学反应的低压区域（p<20 GPa）,这两种混合体系的冲击压缩曲线的差别并不明显;（2）在发生石墨→金刚石相变的高压区域（p>20 GPa）,这两种混合体系的冲击压缩曲线显著不同,且石墨-水体系更易压缩;（3）在45～60 GPa强冲击压力范围内,冲击波诱发的化学反应也不会显著影响这两种体系冲击压缩曲线的走势。上述结论与文献（高压物理学报,1999,13(2):87-92）发表的实验结果相矛盾。进一步分析了引起理论与实验结果不一致的可能原因,并对文献中的实验结果及其理论分析结论提出质疑。     

Experimental constraints on the phase diagram of elemental zirconium

The phase diagram of zirconium metal has been studied using synchrotron X-ray diffraction and time-of-flight neutron scattering at temperatures and pressures up to 1273 K and 17 GPa. The equilibrium phase boundary of the α-ω transition has a dT/dP slope of 473 K/GPa, and the extrapolated transition pressure at ambient temperature is located at 3.4 GPa. For the ω-β transition, the phase boundary has a negative dT/dP slope of 15.5 K/GPa between 6.4 and 15.3 GPa, which is substantially smaller than a previously reported value of −39±5 K/GPa in the pressure range of 32-35 GPa. This difference indicates a significant curvature of the phase boundary between 15.3 and 35 GPa. The α-ω-β triple point was estimated to be at 4.9 GPa and 953 K, which is comparable to previous results obtained from a differential thermal analysis. Except for the three known crystalline forms, the β phase of zirconium metal was found to possess an extraordinary glass forming ability at pressures between 6.4 and 8.6 GPa. This transformation leads to a limited stability field for the β phase in the pressure range of 6-16 GPa and to complications of high-temperature portion of phase diagram for zirconium metal.     

Raman spectra for hydrogen hydrate under high pressure: Intermolecular interactions in filled ice Ic structure

Raman studies of a high-pressure structure of hydrogen hydrate, a filled ice Ic structure, were performed using a diamond anvil cell in the pressure range 3.2-44.1 GPa. The Raman spectra of a vibron revealed that extraction of hydrogen molecules from the filled ice Ic structure occurred above 20 GPa. In addition, the Raman spectra of a roton revealed that a rotation of hydrogen molecules in the filled ice Ic structure was suppressed at around 20 GPa and then the rotation recovered, and the rotation of hydrogen molecules was suppressed again above 35.5 GPa. These results indicate that intermolecular interactions increased between guest hydrogen molecules and host water molecules at around 20 and 35.5 GPa. These intermolecular interactions were considered to be induced to stabilize the filled ice Ic structure. Above 40 GPa, symmetrization of hydrogen bond was considered to contribute to the stability of hydrogen hydrate.     

Electronic band gap of SrSe at high pressure

The electronic band gap of SrSe, in the CsCl-stuctured phase, was measured to 42 GPa via optical absorption studies. The indirect electronic band gap was found to close monotonically with pressure for the range of pressures studied. The change in band gap with respect to pressure, dE_gap/dP, was determined to be −6.1(5)×10⁻³ eV/GPa. By extrapolation of our line fit, we estimate band gap closure to occur at 180(20) GPa.     

Electrical property and phase transition of CdSe under high pressure

In situ electrical resistivity measurement of CdSe was performed under high pressure and moderate temperature using a diamond anvil cell equipped with a microcircuit. With the pressure increasing, a sharp drop in resistivity of over two orders of magnitude was observed at about 2.6 GPa, it was caused by the transition to the rock-salt CdSe. After that, the resistivity decreased linearly with pressure. However, in different pressure range, the decreasing degree was obviously different. This attributed to the different electron structures. By fitting to the curve of pressure dependence of resistivity in different pressure range, the relationship of the band gap to pressure was given and the metallization pressure was speculated to be in the range of 70-100 GPa. The temperature dependence of resistivity showed that in the experimental temperature and pressure range the resistivity had a positive temperature coefficient.     

Phase Transition and Melting Curves of Calcium Fluoride via Molecular Dynamics Simulations

The phase transition and melting curves of CaF2 are investigated by using the general utility lattice programme （CULP） via the shell model with molecular dynamics method. By calculating the entropy H （at OK） and Cibbs free energy G^＊ （at 30OK）, we find that the phase transition pressure from the face-centred cubic （fee） structure to the orthorhombic structure is 11.40 CPa and 9.33 CPa at OK and 300K, respectively. The modified melting point of the fee CaF2 is in the range of 1650-1733K at OCPa. All these results are well consistent with the available experimental data and other theoretical results. We also obtain that the melting temperature of high pressure phase is 990-1073 K at 10 CPa. Moreover, the temperature dependences of the elastic constants Cij, bulk module B and shear module G are also predicted.     

The band gap and electrical resistivity of FeS2-pyrite at high pressures

The indirect energy gap and electrical resistivity of FeS₂-pyrite have been measured at high pressures and 300 K using optical absorption spectroscopy and electrical conductivity measurements. Absorption spectra extend to ∼28 GPa, while resistivity is determined to ∼34 GPa. The band gap of FeS₂ is indirect throughout this pressure range and decreases linearly with pressure at a rate of −1.13(9)×10⁻² eV/GPa. If this linear trend continues, FeS₂ is expected to metallize at a pressure of 80(±8) GPa. The logarithm of resistivity also linearly decreases with pressure to 14 GPa with a slope of −0.101(±0.001)/GPa. However, between 14 and 34 GPa, the logarithm of resistivity is nearly constant, with a slope of −0.011(±0.003)/GPa. The measured resistivity of pyrite may be generated predominantly by extrinsic effects.     

Structural Investigation of Solid Methane at High Pressure

High pressure studies of solid methane are performed using both classical simulated annealing and first-principles methods. A series of simulated annealing and geometry optimization reveal a monoclinic P21/b structure with the unit cell containing four methane molecules. The phonon dispersion curves and vibrational density of states indicate that this structure is stable in the pressure range 10-90 GPa. The electronic band structure and density of states show that this structure has not metalized until 90 GPa.     

Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8GPa

The BaW04-17 phase is synthesized at 5.0 GPa and 610~C with a cubic-anvil apparatus and identified by XRD. Raman scattering measurement is carried out to investigate the phase behaviour of a pure BaW04-Ⅱ phase （space group P21/n, Z = 8） under hydrostatic pressures up to 14.8 GPa at ambient temperature. In each spectrum recorded for this phase, 27 Raman modes are observed, and all bands shift toward higher wavenumber with a pressure dependence ranging from 3.8 to 0.2 cm- 1/GPa. No pressure-driven phase transition occurs in the entire pressure range in this study. Our results indicate that the previously reported high pressure phase of Ba WO4 at pressure above about 10 GPa and room temperature （Errandonea et al. Phys. Rev. B 73（2006）224103） is not the BaW04-Ⅱ phase.     

X-ray diffraction study of molybdenum diselenide to 35.9 GPa

In situ high-pressure angle dispersive synchrotron X-ray diffraction studies of molybdenum diselenide (MoSe₂) were carried out in a diamond-anvil cell to 35.9 GPa. No evidence of a phase transformation was observed in the pressure range. By fitting the pressure-volume data to the third-order Birch-Murnaghan equation of state, the bulk modulus, K_0T, was determined to be 45.7±0.3 GPa with its pressure derivative, K′_0T, being 11.6±0.1. It was found that the c-axis decreased linearly with pressure at a slope of −0.1593 when pressures were lower than 10 GPa. It showed different linear decrease with the slope of a −0.0236 at pressures higher than 10 GPa.     

The p–T phase diagram of KNbO3 by a dielectric constant measurement

A dielectric constant measurement was carried out on perovskite-type ferroelectrics KNbO₃ over a wide range of temperature under high pressure. The temperature- and pressure-dependence of the dielectric constant clarified that all temperatures of the transitions from the ferroelectric rhombohedral to orthorhombic, to tetragonal and then to the paraelectric cubic phase, decrease with increasing pressure. These results indicate that the orthorhombic–tetragonal transition takes place at 8.5 GPa and the tetragonal–cubic transition at 11 GPa, at room temperature.