溴仿在冲击压缩下的光辐射及化学反应

 利用多通道光学高温计测量了溴仿在37 GPa到85 GPa压力范围内的温度,并观察了溴仿/单晶氯化钠界面的热驰豫过程。结果发现,当冲击波压力升高到46 GPa时,溴仿的光辐射强度随时间的变化呈现出“双阶梯”或“双台阶”形状的剖面结构,且台阶之间的时间间隔随冲击压力的增高而减小。当压力达到85 GPa时,上述“双台阶”结构消失,呈现为普通的单台阶剖面结构。冲击波温度测量表明,当压力低于50 GPa时,实测温度与Gokulya报道的数据一致;当压力增至76 GPa以上时,冲击波温度出现突跃性增加。结合对溴仿/氯化钠界面上的热驰豫过程的分析,文中提出,溴仿在上述冲击压力区间内发生了一次带有时间驰豫（或化学诱导期）的化学放热反应。     

Influence of impurity hydrogen on the structure and properties of bulk Li and pressure effects

The structure and properties of a 16-atom body-centered cubic lithium cell with an interstitial hydrogen atom are studied using a pseudopotential-plane-wave method within the density functional theory at 0 K and high pressures. The host lattice is dramatically distorted by the introduction of H. Although the hydrogen atom is stable at the tetragonal site in perfect bcc host lattice, it favors the octahedral site formed by six non-equivalent Li atoms after full relaxation of the cell, showing P4/mmm symmetry within the pressures ranging from 0 to 6 GPa. The lattice ratio (a/c) changes irregularly with external pressure at about 3 GPa. The hydrogen band lies in the bottom of the valence band, separated by a gap from the metallic bands, illustrating the electronegativity of hydrogen. High reflectivity in the low frequency area induced by the impurity hydrogen is observed when only interband transitions are taken account of. A dip in reflectivity due to parallel band transitions is observed at ∼0.4 eV. Another dip at ∼4.3 eV appears when external pressure increases over 4 GPa.     

High-precision measurements of the compressibility of chalcogenide glasses at a hydrostatic pressure up to 9 GPa

The volumes of glassy germanium chalcogenides GeSe₂, GeS₂, Ge₁₇Se₈₃, and Ge₈Se₉₂ are precisely measured at a hydrostatic pressure up to 8.5 GPa. The stoichiometric GeSe₂ and GeS₂ glasses exhibit elastic behavior in the pressure range up to 3 GPa, and their bulk modulus decreases at pressures higher than 2–2.5 GPa. At higher pressures, inelastic relaxation processes begin and their intensity is proportional to the logarithm of time. The relaxation rate for the GeSe₂ glasses has a pronounced maximum at 3.5–4.5 GPa, which indicates the existence of several parallel structural transformation mechanisms. The nonstoichiometric glasses exhibit a diffuse transformation and inelastic behavior at pressures above 1–2 GPa. The maximum relaxation rate in these glasses is significantly lower than that in the stoichiometric GeSe₂ glasses. All glasses are characterized by the “loss of memory” of history: after relaxation at a fixed pressure, the further increase in the pressure returns the volume to the compression curve obtained without a stop for relaxation. After pressure release, the residual densification in the stoichiometric glasses is about 7% and that in the Ge₁₇Se₈₃ glasses is 1.5%. The volume of the Ge₈Se₉₂ glass returns to its initial value within the limits of experimental error. As the pressure decreases, the effective bulk moduli of the Ge₁₇Se₈₃ and Ge₈Se₉₂ glasses coincide with the moduli after isobaric relaxation at the stage of increasing pressure, and the bulk modulus of the stoichiometric GeSe₂ glass upon decreasing pressure noticeably exceeds the bulk modulus after isobaric relaxation at the stage of increasing pressure. Along with the reported data, our results can be used to draw conclusions regarding the diffuse transformations in glassy germanium chalcogenides during compression.     

Investigation of polyamorphism in compressed B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass by the direct measurement of the density

Precise measurements of the relative volume change of vitreous B₂O₃ have been performed by the strain-gauge technique at hydrostatic pressures up to 9 GPa. The features of the strain-gauge technique are analyzed and the specificity of the measurements of “relaxed” and “unrelaxed” bulk moduli is discussed. Smeared anomalies of compressibility (at P > 0.5 GPa and P > 5 GPa) and logarithmic relaxation of the glass density are observed. A significant (by several times!) difference has been revealed between the relaxed bulk modulus of glass obtained from the volume measurements and the unrelaxed modulus estimated from the Brillouin spectroscopic data. The measurements of the relative volume change under compression together with the previous structure investigations and computer simulation results reveal the basic features of the phase transitions in B₂O₃ glass. Both direct and reverse transitions are smeared in pressure. The residual densification in glass is not associated with change in the short-range order.     

CuO在高压下的状态方程、电学性质与相变

 在活塞－圆筒式高压装置上研究了CuO在4.5 GPa内的p-V关系，给出了它的状态方程、格临爱森参数γ₀、体积模量B₀以及B₀的压力导数B₀'。在金刚石压砧装置上，采用我们建立的电阻、电容测量方法研究了CuO在22 GPa内电阻、电容与压力的关系。实验结果表明，CuO的电阻和电容在一些压力下都发生了突然的变化。这些变化可能与CuO内部的电子结构和晶界处的结构状态变化有关。     

Structural phase transition in Bi2Te3 under high pressure

Structural change in Bi₂Te₃ under high pressure up to 16.6 GPa has been studied by powder x-ray diffraction. We observed two times of phase transitions at room temperature at the pressures of 8 and 14 GPa, respectively. According to our preliminary result on electrical resistance, it is reasonable to suppose that superconducting transition with T _c =2.8 K at the pressures of 10.2 GPa is observed in phase II. On the other hand, we found anomalies of the pressure dependences of lattice parameters and volume at around 2 GPa, which probably means the change in electrical structure on the Fermi surface.     

Measurements of the complex shear modulus of polymers under hydrostatic pressure usina the quartz resonator method

Abstract

The quartz resonator method measures the complex shear modulus or compliance of viscoelastic materials in the frequency range from 50 kHz to 140 MHz at temperatures between ?150°C and 300°C and pressures up to 1 GPa. This method can be applied to viscous fluids or polymer melts -even in their glassy or seminystalline regime.

The phase diagram of poly(diethylsiloxane) PDES (a mesophase polymer) was determined for two samples with different molecular weight at pressures up to 400 MPa and temperatures between 20°C and 100°C. Phase transitions are indicated by a sharp bend in the shear compliance although the volume effect of the mesophase-isotropic transition vanishes around 80 MPa.

The pressure dependence of the glass relaxation process (in PVAc), was studied by measuring the change of the complex shear modulus with pressure at constant temperatures between 95°C and 145°C and pressures up to 600 MPa. Additionally to the relaxation process, also the pressure dependence of the real part of the shear modulus in the glassy region can be determined for testing the dislocation concept in the meandermodell by W. Pechhold.     

Electrical conductivity and thermal EMF of CsI at high pressures

Abstract

The pressure dependence of thermal EMF and the resistivity-temperature dependence of CsI has been measured at pressures 20-50 GPa. In CsI non-monotonous change of resistivity, thermal EMF and activation energy of charge carriers has been observed at pressures above 40 GPa. The sign of thermal EMF corresponds to the electron conductivity. At pressures below 47 GPa the resistivity-temperature dependence is of the type characteristic of non-degenerate semiconductors, at pressure above 49 GPa it is characteristic of degenerate semiconductors (or metals). The observed properties are connected probably with the continuous distortion of B2 to an hcp-like phase.     

Electrical properties of Cu1−x Ag x GeAsSe3 (x = 0.55–0.65) at low temperatures and high pressures

Chalcogenides Cu_1-xAg_xGeAsSe₃ (x = 0.55–0.65) are synthesized, and their electrical properties are studied at temperatures of 78–400 K and pressures of 15–45 GPa. The compounds are found to be mixed electronic-ionic conductors. Increasing the fraction of silver lead to an increase conductivity and shifts the region of considerable change in electrical properties at high pressures toward even higher pressures.     

不同压制压力下NiFe2O4纳米固体的ESR研究

 以反滴共沉定法制备了NiFe₂O₄纳米微粉，并在不同压力下将其压制成纳成米固体，然后用XRD谱和ESR谱研究了NiFe₂O₄纳米固体结构和界百状态随压制压力的变化。实验结果表明，NiFe₂O₄纳米固体的结构在高压下没有明显的变化，但其ESR谱的共振线宽和g因子值随着压力升高均表示出先逐渐增大至最大值，然手缓慢下降的规律。这种变化可以归因于纳米固体内部界面离子间的磁相互作用在压力的下所发生和变化。这引起实验结果境示，对于NiFe₂O₄纳米固体而言，最佳的成型压力是4.5 GPa，在此压力下，NiFe₂O₄纳米粒子既可以被压制成致密的纳米固体，又能够保留下它们的纳米结构和纳米性质。     

Phase transitions in poly(ethylene oxide) and polystyrene at high pressure

Abstract

The temperature and enthalpy of melting for poly(ethy1ene oxide) have, for the first time, been studied as a fuction of pressure up to 1 GPa by means of differential scanning calorimetry. The initial increase of the temperature of melting with increasing pressure is 64 K/GPa, whereas the enthalpy decreases by 40% in the 1 GPa pressure range. Using Clausius-Clapeyrons equation the volume change on melting is estimated to be 1.5 cm³/mol. The glass transition temperature T_g for polystyrene has also been studied by the same technique for pressures up to 0.1 GPa. The measurements show that T_g increases with increasing pressure by 250 K/GPa.     

Dynamics of the BiTeI lattice at high pressures

Raman measurements of the phonon spectrum of BiTeI at pressures of up to 20 GPa have been performed. A decrease in the linewidth of E² vibration by almost a factor of 2 with an increase in the pressure to 3 GPa has been detected. The frequencies of all four Raman active modes increase monotonically with the pressure. These lines are observed in spectra up to ～8 GPa. Sharp change in the spectrum occurs at pressures of 8–9 GPa, indicating a transition to the high-pressure phase, which holds up to 20 GPa. This transition is reversible and hardly has any hysteresis. A sample in the high-pressure phase is single crystal.     

高压下γ'-Fe4N晶态合金的声子稳定性与磁性

利用基于密度泛函理论的第一性原理研究了高压下有序晶态γ’-Fe₄N合金的晶格动力学稳定性与磁性. 对比没有考虑磁性的γ’-Fe₄N的声子谱, 得出压力小于1 GPa时, 自发磁化诱导了铁磁相γ’-Fe₄N基态晶格动力学稳定. 压力在1.03-31.5 GPa时, Σ线上的点(0.37, 0.37, 0)、对称点X和M 上相继出现了声子谱软化现象. 压力在31.5-60.8 GPa时, 压致效应与自发磁化对诸原子的作用达到了稳定平衡, 表现出了声子谱稳定. 压力大于61.3 GPa时, 随着压力的增大压力诱导体系动力学不稳定性越强. 通过软模相变理论对于γ’-Fe₄N, 在10 GPa下的声学支声子的M点处软化现象的处理, 发现了动力学稳定的高压新相P2/m-Fe₄N. 压力小于1 GPa时高压新相P2/m-Fe₄N 是热力学稳定的相, 且磁矩与γ’-Fe₄N的磁矩几乎相同. 2.9-19 GPa时, P2/m相的焓比γ’相的焓小, 基态结构更稳定. 大于20 GPa时, 两相磁矩几乎相同.     

Test of the Einstein-Debye relation in supercooled dibutylphthalate at pressures up to 1.4 GPa

Broadband dielectric measurements were carried out on di-n-butyl phthalate (DBP) under isothermal conditions at hydrostatic pressures up to 1.6 GPa. A comparison of the dielectric relaxation times with the viscosity revealed that no breakdown of the Einstein-Debye relation is induced by high compression. This absence of any decoupling is attributed to the weak intermolecular cooperativity of DBP and its negligible change with pressure. Because of the latter, the dielectric spectra conform to time-pressure superpositioning.     

多形性相变的分子动力学模拟

 本文利用分子动力学方法研究了KCl晶体在ρ＝ρ₀时的温度相变。面心立方（fcc）和体心立方（bcc）两种结构的径向分布函数随温度的变化的情况说明，在高压下，发生着bcc结构相fcc结构的转变，bcc结构是不稳定的。为了选取合理的势参数，利用了分子动力学程序在T＝0时的性质，计算了NaCl和KCl晶体的零温状态方程，研究了它们在压力作用下发生的多形性相变。计算表明，NaCl和KCl晶体将分别于18.8 GPa和5.9 GPa发生从fcc到bcc的多形性相变，这些值相当接近实验结果。着说明本文选用的势参数势有一定精度的。     

High pressure electrical transport behavior in organic semiconductor pentacene

The high pressure electrical transport behavior of pentacene has been investigated by alternating current impedance techniques and direct current resistivity measurement in a diamond anvil cell (DAC). The resistance decreases with increasing pressure below 17.4?GPa, while it increases above 17.4?GPa, which is caused by the transition of pentacene from an ordered state to the disordered state under higher pressure. From the Raman spectra under various pressures, pentacene becomes amorphous above 17.3?GPa, which is consistent with the impedance results. The charge transport operates in the hopping regime with charges jumping between interacting molecules, and the hopping mechanisms are related to the vibration modes. Above 17.4?GPa, the pressure dependence of the relaxation activation energy is 21.7?meV/GPa and pentacene keeps semiconductor characteristics up to 28.3?GPa.     

Anomalous pressure dependence of the superconducting transition temperature of beta-pyrochlore AOs2O6 oxides

High-pressure effects on the superconducting transitions of beta-pyrochlore oxide superconductors AOs(2)O(6) (A = Cs,Rb,K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature T(c) first increases with increasing pressure in every compound and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa), and 10 K (0.6 GPa) for A = Cs, Rb, and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the coefficient A of the T(2) term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in T(c).     

X-ray Diffraction Study on Pressure-Induced Phase Transformation in Nanocrystalline GaAs

We have shown that the onset and transition pressures of the GaAs I M II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs at the semiconductor-to-metal transition is explained by the two-component model developed by Gleiter.     

Pressure-induced isostructural phase transition in Bi2Sr2CaCu2O8+δ

The high-pressure structures of an underdoped cuprate superconductor Bi₂Sr₂CaCu₂O_8+δ have been studied by synchrotron X-ray diffraction at pressures up to 36.5 GPa. We find that this superconductor retains its orthogonal structure with the space group Amaa in the pressure range studied. Upon compression, both the a and b axes first shrink monotonically up to 17.4 GPa from their ambient pressure values and keep these behaviors with positive compressibilities up to 36.5 GPa after experiencing expansion with negative compressibilities in the pressure regime between 17.4 and 23.7 GPa. However, the c axis decreases continuously with increasing pressure with a slow change at about 23.7 GPa. The results indicate an isostructural phase transition starting at 17.4 GPa and a structural collapse at around 23.7 GPa.     

High pressure studies up to 50GPa of CuO

Abstract

Copper oxide has been studied at high pressure up to 50 GPa. A monoclinic structure was compatible with the measurements at all pressures, and no phase change was observed. A bulk modulus, B₀, = 98 GPa, and its pressure derivative B′₀ = 5.6 was obtained.