硫化铁的两个电导率相关的相变

 由于X射线对高级相变和电子相变不够敏感,致使很多物质的相变和新的性质被忽略。对物质电阻的变化进行分析可以很好地弥补这一缺陷。通过金刚石对顶砧上原位电阻测量方法,在0~88.7 GPa的压强范围内,在300~443 K的温度条件下,基于范德堡法电阻测量原理,对硫化铁的电导率进行了测量。通过对电导率的分析发现,在零压、温度为408 K的条件下,硫化铁转变成了NiAs结构相。在34.7 GPa和61.3 GPa压强处发现了两个新的突变点,为了印证这两处相变的可靠性,分别测量了在不同压强下样品电导率随温度的变化情况。     

Electron Transport Property of CdTe under High Pressure and Moderate Temperature by In-Situ Resistivity Measurement in Diamond Anvil Cell

In situ resistivity measurement has been performed to investigate the electron transport property of powered CdTe under high pressure and moderate temperature in a designed diamond anvil cell. Several abnormal resistivity changes can be found at room temperature when the pressure increases from ambient to 33 GPa. The abnormal resistivity changes at about 3.8 GPa and 10 GPa are caused by the structural phase transitions to the rock-salt phase and to the Cmcm phase, respectively. The other abnormal resistivity changes at about 6.5 GPa, 15.5 GPa, 22.2 GPa and about 30 GPa never observed before are due to the electronic phase transitions of CdTe. The origin of the abnormal change occurred at about 6.5 GPa is discussed. The temperature dependence of the resistivity of CdTe shows its semiconducting behaviour at least before 11.3 GPa.     

T1系单相超导材料的高氧压合成及压力对超导性的影响

 系统地研究了在0~3 MPa氧压下T1系超导材料的制备过程及其超导性质。结果表明：0.25~0.90 MPa氧压下所制备的样品为纯2223相，T_c0最高可达125.3 K；1.45~3.00 MPa氧压下样品为纯2212相，T_c0在95~100 K之间；0.90~1.45 MPa氧压下样品为2223及2212两相共存。对两种单相样品的高压研究结果表明，2223相样品比2212相样品有着较强的压力效应，在0~0.52 GPa压力下分别为4.0 K/GPa及2.0 K/GPa。     

Structural phase transformation of GaN under high-pressure: an exact exchange study

The phase transformation of GaN under high pressure is theoretically studied in the KS-DFT framework using the EXX method. Both KLI and LDA pseudopotentials were tried. The LDA-PP result for the transition pressure is 41.7 GPa while that of the KLI-PP is 41.5 GPa. Both results are in a very good agreement with the latest experimental value of 42 GPa. The effect of the nonlinear core correction is found to be small but not negligible.     

原位高压微米氧化锌电学性质的研究

利用集成有金属薄膜电极的金刚石对顶砧,对微米氧化锌样品进行了原位高压电导率测量.结果表明,在919 GPa时样品电导率达到最小值,在919—1122 GPa时样品电导率急剧增大,说明此时样品从纤锌矿结构向岩盐矿结构转变直至完全相变,1122　GPa为相变点.通过测量不同条件下高温退火处理的样品电导率,明显看到氧空位对电导率的影响. 关键词： 高压 微米氧化锌 电导率 金刚石对顶砧     

压力淬火过程中锗的相结构研究

 应用高压原位差热方法，直接测量了压力下锗的固化参数─—固化温度与过冷度。高压差热信号表明，当压力大于3 GPa时，锗在凝固过程中可能发生结构相变。X射线结构分析表明，在最终的样品中除GeⅠ相外，还形成GeⅢ相和GeⅣ相。     

High-Pressure Phase Relationships for FeS

Phase relationships for FeS polymorph have been studied at the pressure of 16-20 GPa and temperature of 300-1350 K by in situ X-ray observation using a large volume high-pressure apparatus and a synchrotron radiation. Contrary to Fei's prediction [1], we found the stability field of NiAs-type phase of FeS extending at least to 18 GPa. Results of in situ X-ray observation correspond with the NiAs-hexagonal phase boundary determined by Kusaba et al . [2, 3]. Assuming the straight NiAs-hexagonal phase boundary, we estimate that the NiAs-hexagonal-liquid triple junction is located at 39.5 GPa and 2300 K.     

In-Situ High Pressure Raman Spectrum and Electrical Property of PbMoO4

In-situ high pressure Raman spectra and electrical conductivity measurements of scheelite-structure compound PbMoO4 are presented. The Raman spectrum of PbMoO4 is determined up to 26.5 GPa on a powdered sample in a diamond anvil cell （DAC） under nonhydrostatic conditions. The PbMoO4 gradully experiences the trans- formation from the crystal to amorphous between 9.2 and 12.5 GPa. The crystal to amorphous transition may be due to the mechanical deformation and the crystalographic transformation. Furthermore, the electrical conductivity of PbMoO4 is in situ measured accurately using a microcircuit fabricated on a DAC based on the van der Pauw method. The results show that the electrical conductivity of PbMoO4 increases with increases of pressure and temperature. At 26.5 GPa, the electrical conductivity value of PbMoO4 at 295K is 1.93 - 10-4 S/cm, while it raises by one order of magnitude at 430K and reached 3.33 - 10-3 S/cm. However, at 430K, compared with the electrical conductivity value of PbMoO4 at 26.5 GPa, it drops by about two order magnitude at 7.4 GPa and achieves 2.81 × 10^-5 S/cm. This indicates that the effect of pressure on the electrical conductivity of PbMoO4 is more obvious than that of temperature.     

Semiconductor-metal transition in selenium under shock compression

Phase transitions in selenium are studied by time-resolved measurements of the electrical conductivity under shock compression at a pressure of up to 32 GPa. The pressure dependence of the electrical conductivity (σ(P)) has two portions: a sharp increase at P < 21 GPa and a plateau at P > 21 GPa. The experimental data and the temperature estimates indicate that, at P < 21 GPa, selenium is in the semiconductor state. The energy gap of semiconducting selenium decreases substantially under compression. At P > 21 GPa, the electrical conductivity saturates at ～10⁴ Ω^?1 cm^?1. Such a high value of the electrical conductivity shows the effective semiconductor-metal transition taking place in shock-compressed selenium. Experiments with samples having different initial densities demonstrate the effect of temperature on the phase transition. For example, powdered selenium experiences the transition at a lower shock pressure than solid selenium. Comparison of the temperature estimates with the phase diagram of selenium shows that powdered selenium metallizes in a shock wave as a result of melting. The most plausible mechanism behind the shock-induced semiconductor-metal transition in solid selenium is melting or the transition in the solid phase. Under shock compression, the metallic phase arises without a noticeable time delay. After relief, the metallic phase persists for a time, delaying the reverse transition.     

High-Pressure Phase Transition in Cyclo-octane

Structural behaviour of cyclo-octane under high pressure is studied by using a synchrotron x-ray source in a diamond anvil cell （DAC） up to 40.2 GPa at room temperature. The cyclo-octane firstly solidifies to the triclinic phase at 0.87 GPa. With the increasing pressure, the phase of cyclo-octane changes to the tetragonal phase at about 6.0 GPa and then transforms to amorphous phase above 18.2 GPa, which is kept till to 40.2 GPa. All the phase transitions of cyclo-octane are irreversible.     

Fe3O4/β-CD的高压电学性质研究

 高压下的电学性质测量是获得材料物理性质的有效手段。利用集成在金刚石对顶砧上的薄膜微电路,测量了高压下Fe₃O₄/β-CD（β-糊精）的电导率,并分析了电导率随压力的变化关系。在0～39.9 GPa范围内,Fe₃O₄/β-CD的电导率随压力的增加而逐渐增大,并呈半导体的特征;而在17.0 GPa处其电导率发生突变,表明样品发生了高压相变。在卸压过程中,电导率随压力的变化呈线性关系,并且卸压后样品的电导率不能回到最初的状态,推测这是一个不可逆的高压结构相变。     

Bonding in the superionic phase of water

The predicted superionic phase of water is investigated via ab initio molecular dynamics at densities of 2.0--3.0 g/cc (34-115 GPa) along the 2000 K isotherm. We find that extremely rapid (superionic) diffusion of protons occurs in a fluid phase at pressures between 34 and 58 GPa. A transition to a stable body-centered cubic O lattice with superionic proton conductivity is observed between 70 and 75 GPa, a much higher pressure than suggested in prior work. We find that all molecular species at pressures greater than 75 GPa are too short lived to be classified as bound states. Up to 95 GPa, we find a solid superionic phase characterized by covalent O-H bonding. Above 95 GPa, a transient network phase is found characterized by symmetric O-H hydrogen bonding with nearly 50% covalent character. In addition, we describe a metastable superionic phase with quenched O disorder.     

十种稀土金属电阻的压力效应

 使用Bundy和Dunn发展起来的带有烧结金刚石砧的Drickamer型高压装置，用固定点测压法标定实验压力，在室温及0~43 GPa的压力范围内测量了稀土金属中Pr、Nd、Sm、Gd、Tb、Dy、Ho、Tm、Lu和Yb的电阻随压力的变化。在各稀土元素的电阻随压力变化的曲线上，观测到了若干“凸起”和斜率突变点，根据Jayaraman提出的三价稀土在压力作用下的相变顺序，得到了这些突（凸）变点分别对应着hcp→Sm-type→dhcp→fcc相变顺序中的某一类型的相变压力。此外还观测到了Pr、Gd、Tb的fcc相随着压力再增高而发生的相变，根据已报导的关于Pr的工作，推测Gd和Tb的这一相变应为fcc→dfcc相变，它们分别发生在22.0和24.5 GPa。在本工作所得结果基础上对Johansson的三价稀土总相图进行了修正。     

Structural Evolution of Compressing Amorphous Ice

Molecular dynamics simulation is employed to study structural evolution during compressing low density amorphous ice from one atmosphere to 2.5 GPa. The calculated results show that high density amorphous ice is formed under intermediate pressure of about 1.0GPa and O-O-O angle ranges from about 83°to 113° and O-H…O is bent from 112° to 160°The very high density amorphous ice is also formed under the pressure larger than 1.4 GPa and interstitial molecules are found in 0.3-0.4 A just beyond the nearest O-O distance. Low angle O-H… O disappears and it is believed that these hydrogen bonds are broken or re-bonded under high pressures.     

Measurement of Seebeck effect (thermoelectric power) at high pressure up to 40 GPa

The paper reports details of a high-pressure thermoelectric power (Seebeck effect) technique up to 40 GPa. Several different types of high-pressure cells with anvil insets are presented. The technique was applied for measurements of pressure dependence of the thermopower of several substances including elemental metals (lead, Pb; indium, In), cerium-nickel alloy, Ce-Ni and sulphur, S. Two peculiarities in the pressure dependences of the thermopower of CeNi were found and attributed to structural transformations, near ∼5 and ∼10 GPa. These transitions were confirmed in direct X-ray diffraction studies. Sulphur compressed to 40 GPa exhibited a hole type conductivity and the thermopower value was about ∼+1 mV/K. Additionally, as an example of pressure calibration, the data on the electrical resistivity of zinc selenide, ZnSe, are given in a range of 0-23 GPa. These data suggest three possible scenarios of phase transitions from a rock salt (RS) high-pressure phase of ZnSe under decompression: RS→zinc blende (ZB), RS→cinnabar→ZB, and RS→wurtzite.     

高压下铁的电导率及X射线衍射研究

 用四点电极法及磁控溅射结合光刻集成电极的方法，测量了铁在25 GPa压力下的电阻随压力的变化；用微区X射线衍射仪原位测量了铁在25 GPa压力下晶胞参数随压力的变化关系。实验结果表明，铁在13.7 GPa时发生相变，由体心立方相转变为六方密堆相，在18.1 GPa时相变结束。利用高压下铁的电阻数据，结合X射线衍射结果，推导出铁的电导率随压力的变化关系。     

Phase transitions in CsHSO4 up to 2.5 GPa: Impedance spectroscopy under pressure

Phase transitions in CsHSO₄ at pressures up to 2.5 GPa have been studied with the help of electrical impedance measurements. The phase boundaries have been identified with the help of calculated activation energies of electrical conductivity and dielectric relaxation time. The derived temperatures of phase transition from the low conductive phase II into super ionic phase I at pressure less than 1 GPa confirm the previous results of Ponyatovski? et al. (1985) [4] and Friesel et al. (1989) [27]. The phase diagram derived in this study for pressure larger than 1 GPa differs from the data of Ponyatovski? et al. (1985) [4]. The phase transitions IV-VI and VI-I occur at higher temperatures having significantly larger Clapeyron slope. The phase VII was not identified from heating cycle and appears only under cooling between phases I and VI. The phase VIII was detected at 2.5 GPa at T<350 K and only during heating.     

金刚石对顶砧原位电导率测量系统

 在金刚石对顶砧中进行原位高温高压电阻测量时,由于受到绝热层的限制,从而达不到理想的温度条件。采用普通的粉末绝热材料,会给电极的引入造成很大困难,而且不规则的电阻丝使电阻测量很难精确量化。利用溅射镀膜方法,在对顶砧的砧面上镀氧化铝膜作绝热层,溅射的金属钼膜作电极材料,成功地完成了高温高压条件下原位电阻的测量。利用此装置,测量了铁镁硅酸盐(Mg_0.875,Fe_0.125)₂SiO₄在高温高压环境下（31~35 GPa,1 500~3 400 K）的电导率,得到了样品的导电粒子激活能,发现其激活能随着压强的升高而增大,与低压低温（小于15 GPa,低于1 200 K）条件相比,其激活体积和激活能都明显减小。     

非晶锂离子导体在高压下的电特性

 本文首次测量了非晶态锂离子导体B₂O₃-0.7Li₂O-0.7LiCl-xAl₂O₃（x=0.05及0.15）在0.000 1~0.80 GPa压力下的离子电导率及激活体积，发现激活体积在一定压力下由负变正，并用离子迁移通道的物理图象给出初步的微观解释。此外，还比较了整片非晶与粉末压片的异同，以及氧化铝组分不同对压力相变点的影响。观测到压力增强及卸压后电导率的弛豫现象——减至常压后离子电导比加压前提高10.4倍。     

Ionic to electronic dominant conductivity in Al2(WO4)3 at high pressure and high temperature

Electrical conduction and crystal structure of Al₂(WO₄)₃ at 400 °C have been studied as a function of pressure up to 5.5 GPa using impedance methods and synchrotron radiation X-ray diffraction, respectively. AC impedance spectroscopy and DC polarization measurements reveal an ionic to electronic dominant transition in electrical conductivity at a pressure as low as 0.9 GPa. Conductivity increases with pressure and reaches a maximum at 4.0 GPa, where the conductivity value is 5 orders of magnitude greater than the 1 atm value. Upon decompression, the conductivity retains the maximum value until the sample is cooled at 0.5 GPa. The high pressure-temperature X-ray diffraction results show that the lattice parameters decrease as pressure increases and the crystal structure undergoes an orthorhombic to tetragonal-like transformation at a pressure ∼3.0 GPa. The change of conduction mechanism from ionic to electronic may be explained by means of pressure-induced valence change of W⁶⁺→W⁵⁺, which results in electron transfer between W⁵⁺-W⁶⁺ sites at high pressure.