Acoustic behaviour and equation of state of amorphous ethylene–vinyl acetate copolymer studied by means of high-pressure Brillouin scattering spectroscopy

The determination of the equation of state (EOS) of amorphous materials is very important for fundamental understanding of the glass transition and applications as well. Simultaneous observation of both longitudinal and transverse acoustic modes by Brillouin scattering spectroscopy has been one of the major methods to obtain EOS of amorphous materials. However, the transverse acoustic mode is hardly seen from some of the amorphous polymers, which makes it difficult to derive EOS. The temperature and pressure dependences of the acoustic properties of amorphous ethylene–vinyl acetate (EVA) copolymer were measured by using high-pressure Brillouin scattering spectroscopy. The temperature variation induced large changes in the frequency shift and linewidth of the longitudinal acoustic mode due to strong coupling between the structural relaxation process and the propagating density fluctuations. The residual linewidth in the glassy state was attributed to the remnant intramolecular motions of EVA, the activation energy of which was estimated to be ～3.30 ± 0.27 kcal/mol. The pressure–density relationship of EVA could be obtained for the first time by measuring the refractive index and using the Lorentz–Lorenz equation. The density and the refractive index exhibited monotonic increase up to approximately 12 GPa. The strong reduction of the acoustic damping at low pressures below ～3 GPa was attributed to the collapsing free volume in EVA. The present study clearly shows that measuring the refractive index by high-pressure Brillouin spectroscopy may be an alternative method to get the EOS of polymeric materials whose transverse acoustic mode is too weak to be observed.     

High-pressure elasticity of poly(methyl methacrylate) up to 31.5 GPa studied by Brillouin spectroscopy

High-pressure acoustic properties of poly(methyl methacrylate) (PMMA) was investigated up to 31.5 GPa by using a Fabry-Perot interferometer and a diamond anvil cell. Both backscattering and forward, symmetric scattering geometries were used to derive the pressure dependences of the longitudinal sound velocity, the refractive index, and the density over the investigated pressure range. These physical properties showed rapid increases upon compression up to ∼5 GPa, above which they exhibited sluggish increases upon further increase. The crossover behavior at ∼5 GPa was attributed to the change in the densification of PMMA caused by complete collapse of free volume in this polymeric material.     

High‐pressure Brillouin study of the elastic properties of rare‐gas solid xenon at pressures up to 45 GPa

The pressure dependences of three adiabatic elastic constants, adiabatic bulk modulus, refractive index, and elastic anisotropy, as well as Cauchy deviation of fcc solid Xe have been determined up to 10 GPa at 296 K by high‐pressure Brillouin scattering spectroscopy. The characteristics of elastic properties at high pressure of rare‐gas solid Xe are investigated by comparison with the previous studies on Ne, Ar, and Kr. Above 10 GPa, the occurrence of splitting in the Brillouin signals and the direction dependence of acoustic velocities for solid Xe clearly show partial phase transformation to the hcp structure reported by the previous X‐ray diffraction and Raman scattering studies. The shear elastic modulus in the hcp phase of solid Xe has also been estimated at pressures up to 45 GPa by using the pressure dependence of the Raman wavenumber shift for the E_2g mode. Copyright © 2008 John Wiley & Sons, Ltd.     

High pressure study of acetophenone azine

High pressure Raman spectra of acetophenone azine (APA) have been measured up to 17.7 GPa with a diamond anvil cell. Two crystalline-to-crystalline phase transformations are found at pressures about 3.6 and 5.8 GPa. A disappearance of external modes and the C–H vibration at pressures higher than 8.7 GPa suggests that the sample undergoes a phase transition to amorphous or orientationally disordered (plastic) state, and the amorphization was completed at about 12.1 GPa. The disordered state is unstable and, then, a polymerization transformation reaction occurs with a further pressure increase. After the pressure has been released, the polymerization state can remain at the ambient condition, indicating that the virgin crystalline state is not recovered. The results show that the phenomenon underlying the pressure induced phase transition of APA may involve profound changes in the coordination environments of the symmetric aromatic azine.     

In situ Brillouin spectroscopy of a pressure-induced apparent second-order transition in a silicate glass

Brillouin scattering measurements of a silicate glass, carried out at high pressures in the diamond anvil cell, show a dramatic increase in the pressure dependence of longitudinal velocity, and a discontinuity in the compressibility of the glass at about 6 GPa. While a first-order phase transition has been documented under pressure within amorphous ice, we demonstrate that an apparent second-order transition to a new, structurally distinct amorphous phase can occur via the abrupt onset of a new compressional mechanism, which may be triggered by a shift in polymerization of the glass or an onset of a change in coordination of silicon, within pressurized amorphous silicates.     

Study of cerium phase transitions in shock wave experiments

Cerium has a complex phase diagram that is explained by the presence of structural phase transitions. Experiments to measure the sound velocities in cerium by two methods were carried out to determine the onset of cerium melting on the Hugoniot. In the pressure range 4–37 GPa, the sound velocity in cerium samples was measured by the counter release method using manganin-based piezoresistive gauges. In the pressure range 35–140 GPa, the sound velocity in cerium was measured by the overtaking release method using carbogal and tetrachloromethane indicator liquids. The samples were loaded with plane shock wave generators using powerful explosive charges. The onset of cerium melting on the Hugoniot at a pressure of about 13 GPa has been ascertained from the measured elastic longitudinal and bulk sound velocities.     

Brillouin scattering of vitreous silica under high pressure

The pressure dependence of Brillouin spectra of vitreous silica exhibits a maximum in the hypersonic absorption and a minimum in the sound velocity at about 2 GPa almost independent of temperature. The results are discussed on the basis of relaxing defects residing in double-well potentials with a Gaussian distribution of barrier heights and a Lorentzian distribution in the asymmetry. Our analysis suggests that both the distribution functions are strongly changed at higher pressures. It is striking that a phase boundary between α-quartz and coesite exists just at the pressure where absorption and sound velocity of vitreous silica pass their extremum. This might be a hint that a corresponding structural change also occurs in the glass.     

铜的高压声速和冲击熔化

 用光分析技术，测量了在一维应变冲击条件下，无氧铜的高压下声速，压力范围为125~170 GPa。将上述结果与Broberg、Morris等和Aльгшуер等过去发表的数据结合在一起，对0~170 GPa整个压力区间的声速数据做了综合分析，给出了声速随压力的变化规律。实验结果发现，无氧铜在156~159 GPa之间开始发生冲击熔化，到170 GPa左右，完全进入液相区；对于处于0~156 GPa固体无氧铜的弹性声速c_l可用ln c_l=1.565 888-2.645 488×10^-2ln p+2.710 681×10^-2ln²p拟合公式描述（p的单位为GPa，c_l的单位为km/s），拟合值与实验值的相对误差小于1.3%。     

High P–T Brillouin scattering study of H2O melting to 26 GPa

The properties of solid and liquid phases of H₂O at high pressure and temperature remain an active area of research. In this study, Brillouin spectroscopy has been used to determine the temperature dependence of sound velocities in H₂O as a function of pressure up to 26 GPa through the phase field of ice VII and into the liquid to a maximum temperature of 1200 K. The Brillouin shift of the quasi-longitudinal acoustic mode moves to lower frequencies upon melting at each pressure. As a test of the method, measurements of the melting of Ar by Brillouin scattering at several pressures show a similar behavior for the acoustic mode, and measured melting points are consistent with previous results. The results of H₂O melting are consistent with previously reported melting curves below 20 GPa. The data at higher pressure indicate that ice melts at a higher temperature than a number of previous studies have indicated.     

一种高密度玻璃的多形性高压相变和物态方程研究

在二级轻气炮上用无氧铜飞片直接撞击重玻璃平板样品(密度为4.817 g/cm³,材料牌号:ZF6)开展了冲击压缩实验研究,压力范围为52.1—167.8 GPa,并采用多通道瞬态辐射高温计和光分析技术测量了其雨贡纽线、高压声速和冲击波温度等动态特性.实验结果显示,上述性质在三个不同压力区间出现不连续性变化,表明冲击压缩下该样品材料存在多形性高压相变,相变起始压力分别为23,78和120 GPa.实测声速先是随冲击压力的增高而增加,并在78 GPa附近出现急剧下降,之后又随压力增长,并在120 GPa之后下降到体波声速,表明材料进入高压熔化相.温度数据同样在78和120 GPa处出现明显的不连续变化,并在120 GPa之后变化趋于平缓与计算的Lindeman熔化线相符,进一步印证了上述相变行为.实测雨贡纽数据与LASL数据库中的重玻璃数据相符,结果显示除23 GPa附近有一明显的突变外,高压区数据几近线性变化,表明重玻璃的两个高压相变均为二级相变.本文报道的重玻璃材料高压物性数据和序列相变认识对于发展反向加载技术、提高材料声速测量精度和适用压力范围具有实用价值. 关键词： 重玻璃 冲击温度 卸载声速 冲击相变     

低孔隙度疏松锡的高压声速与相变

为研究微孔洞对锡的高压相变的影响, 对含亚微米孔洞的疏松锡(疏松度m=1.01)进行了冲击加载-卸载实验. 利用DPS(Doppler pins system)测得了31.8-66.1 GPa冲击压力下疏松锡/LiF界面粒子的速度剖面, 获得了各压力下的纵波声速与体波声速, 给出了该疏松锡的冲击熔化起始压力约为49.1 GPa, 获得了各压力下的剪切模量与泊松比. 结合密实锡与疏松锡的高压纵波声速、体波声速与剪切模量, 界定密实锡的冲击熔化压力在53.5-62.3 GPa之间, 高于疏松锡的值, 表明微孔洞明显降低了冲击熔化压力. 对密实锡准确的冲击熔化压力值还需要进一步的实验数据. 测试的固态压力范围内的声速数据没有明显奇异点, 表明疏松锡没有类似密实锡的固态bcc 相变发生.     

低孔隙度疏松铝的高压声速与冲击熔化

对含微孔洞疏松度m=1.04的疏松铝进行了冲击加载-卸载实验,利用DISAR(distance interferometer system for any reflector)测得了53至99 GPa五个冲击压力下疏松铝/LiF界面粒子速度波剖面,获得了各压力下的纵波声速和其中三个压力点的体波声速,确定出疏松铝的冲击熔化压力约为81 GPa,确定出高压下冲击熔化前的泊松比约为0.372.通过分析,微孔洞明显降低了冲击熔化压力,引起的非谐振效应明显,状态方程计算中考虑非谐效应,非谐因子l 关键词： 低孔隙度 疏松铝 声速 冲击熔化     

High-pressure Raman and infrared study of ZrV 2O7

The room-temperature Raman and infrared spectra of zirconium vanadate (ZrV ₂O₇) were observed up to pressures of 12 GPa and 5.7 GPa, respectively. The frequencies of the optically active modes at ambient pressure were calculated using direct methods and compared with experimental values. Average mode Grüneisen parameters were calculated for the Raman and infrared active modes. Changes in the spectra under pressure indicate a phase transition at ∼1.6 GPa, which is consistent with the previously observed α (cubic) to β (pseudo-tetragonal) phase transition, and changes in the spectra at ∼4 GPa are consistent with an irreversible transformation to an amorphous structure.     

Phase transformations in amorphous fullerite C60 under high pressure and high temperature

First phase transformations of amorphous fullerite C₆₀ at high temperatures (up to 1800 K) and high pressures (up to 8 GPa) have been investigated and compared with the previous studies on the crystalline fullerite. The study was conducted using neutron diffraction and Raman spectroscopy. The amorphous fullerite was obtained by ball-milling. We have shown that under thermobaric treatment no crystallization of amorphous fullerite into С₆₀ molecular modification is observed, and it transforms into amorphous-like or crystalline graphite. A kinetic diagram of phase transformation of amorphous fullerite in temperature–pressure coordinates was constructed for the first time. Unlike in crystalline fullerite, no crystalline polymerized phases were formed under thermobaric treatment on amorphous fullerite. We found that amorphous fullerite turned out to be less resistant to thermobaric treatment, and amorphous-like or crystalline graphite were formed at lower temperatures than in crystalline fullerite.     

Hypersonic velocity measurement using Brillouin scattering technique. Application to water under high pressure and temperature

This paper presents recent improvement on sound velocity measurements under extreme conditions, illustrated by the hypersonic sound velocity measurements of water up to 723 K and 9 GPa using Brillouin scattering technique. Because water at high pressure and high temperature is chemically very aggressive, these experiments have been carried out using a specific experimental set-up. The present data should be useful to better constrain the water equation of state at high density. This new development brings high-quality elastic data in a large pressure/temperature domain, which may afterwards benefit the understanding of many other fields as nonlinear acoustics, underwater sound, or physical acoustics from a more general point of view.     

钒的高压声速测量

采用反向碰撞方法进行了钒冲击实验,利用激光干涉测速技术对V/LiF窗口界面粒子速度剖面进行测量.通过对粒子速度剖面的分析获得了32—88 GPa压力范围内钒的高压声速.实验获得的声速-冲击压力关系在约60 GPa存在间断,表明钒发生了冲击相变.相变压力与静高压实验结果及第一性原理计算结果基本一致.     

Study of monazite under high pressure

Monazite was studied under high pressures of up to 20 GPa and 12 GPa by using synchrotron X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction data suggested that there was a structural distortion at ～11.5 GPa. The pressure–volume data of the monazite was fitted to a third-order Birch–Murnaghan equation of state and yielded a bulk modulus of 109(1) GPa and a pressure derivative of 6.7(1), in agreement with an empirical formula.     

Brillouin scattering study of methanol at high pressure

Abstract

Brillouin scattering has been used to study methanol as a function of pressure up to 8.4 GPa. Our near-forward-scattering experiments yield the pressure dependence of the velocity of longitudinal acoustic (LA) phonons, while we determine the pressure dependence of the product of the index of refraction and the LA phonon velocity from our backscattering experiments. The pressure dependence of the LA phonon lifetimes is obtained from the linewidth of the measured Brillouin peaks. From our backscattering experiments we find that the normalized phonon attenuation is a decreasing function of pressure.     

动高压下拉格朗日声速的测定及其应用

 通过实时记录冲击加载—再加载和冲击加载—卸载波的粒子速度剖面,得到了再加载和卸载波在93W合金中传播的拉格朗日声速。通过拉格朗日声速从准弹性到纯塑性的转化,获得了材料在一次冲击终态时的剪应力、剪切模量以及考虑了剪应力修正后的93W合金的冲击绝热关系。     

静水压加载单晶MgO的超声测量与压力标定

通过对单晶MgO的高压声速测量,结合高压Brillouin散射数据,对静水压加载条件下六面顶压机高压腔中的压力进行了多点系统标定(系统油压从15 MPa到51 MPa,间隔2 MPa),建立了新的大腔体压机超声测量和压力标定技术。相比传统的仅采用2~3个标定压力点的方法,该技术在统计上更加可靠。结合LY12铝的高压声速测量,进一步验证了该压力标定方法的合理性。与固体传压组装相比,固液混合传压组装在相同油压下的压力值系统偏低,分析认为这主要是由于固体传压介质中的剪切效应导致标定压力值系统偏高造成的。