Effect of pressure on electrical resistance of WSe<Subscript>2</Subscript> single crystal

The results of electrical resistance measurements under pressure on single crystals of WSe₂ are reported. Measurements up to 8.5 GPa are carried out using Bridgman anvil set up and beyond it using diamond anvil cell (DAC) up to a pressure of 27 GPa. There is no clear indication of any phase transition till the highest pressure is reached in these measurements.     

Growth and high pressure studies of zirconium sulphoselenide single crystals

Transition metal trichalcogenides are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transition under pressure. In this paper authors reported the details about synthesis and characterization of zirconium sulphoselenide single crystals. The chemical vapour transport technique was used for the growth of zirconium sulphoselenide single crystals. The energy dispersive analysis by X-ray (EDAX) gave the confirmation about the stoichiometry of the as-grown crystals and other structural characterizations were accomplished by X-ray diffraction (XRD) study. The variation of electrical resistance was monitored in a Bridgman opposed anvil set-up up to 8 GPa pressure to identify the occurrence of any structural transition. These crystals do not possess any structural transitions upto the pressure limit examined.     

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.     

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。     

High pressure investigations on amorphous selenium

We report the diamond anvil cell (DAC) high pressure powder X-ray diffraction studies on amorphous selenium (a-Se) under truly hydrostatic pressure condition up to 20 GPa. Amorphous selenium exhibits a sharp and irreversible transition to a hexagonal structure at 10.6 ± 0.1 GPa. It is also known that metallization occurs in a-Se around this pressure. Some plausible arguments are provided to suggest that the amorphous to crystalline transition may be driven by metallization.     

Strength and equation of state of molybdenum triboride under 80 GPa pressure,using radial X-ray diffraction

The strength and equation of state of molybdenum triboride have been determined under nonhydrostatic compression up to 80?GPa, using an angle-dispersive radial X-ray diffraction technique in a diamond anvil cell (DAC). The RXD data yield a bulk modulus and its pressure derivative as K_0?=?342(6)?GPa with K₀′?=?2.11(17) at ψ?=?54.7°. Analysis of diffraction data using the strain theory indicates that the ratio of differential stress to shear modulus (t/G) ranges from 0.002 to 0.050 at pressures of 4–80?GPa. Together with theoretical results on the high pressure shear modulus, our results here show that molybdenum triboride sample under uniaxial compression can support a differential stress of ～10?GPa when it started to yield with plastic deformation at ～30?GPa. In addition, we draw a conclusion that MoB₃ is not a superhard material but a hard material.     

Structural transformations in single-wall carbon nanotubes under high pressure

Single-wall carbon nanotubes (SWNTs) under high pressure exhibit high structural stability and a series of structural transitions up to 35 GPa. As theoretically predicted, the irreversible transformation of SWNTs in the pressure range of 10–30 GPa can be attributed to the polymerization of nanotubes. The electrical conductivity of SWNTs is studied at high pressures up to 35 GPa using a diamond anvil cell (DAC) with electrically conductive anvils of the “rounded cone-plane” type made of synthetic carbonado-type diamonds. SWNTs are studied before and after the application of high pressure using the Raman confocal microscopy technique. Analysis of Raman spectra and pressure dependences of the SWNT resistance shows that the observed structural changes in SWNTs are reversible and no polymerization or collapse are observed.     

Resistance anomaly and structural disorder in NiSi2 under high pressure

Results of X-ray diffraction, electrical resistance, thermoelectric power measurements and electronic band structure calculations on NiSi₂ under high pressure are reported. The thermoelectric power (TEP) changes sign near 0.5 GPa (from +30 to −20 μV/K). As the pressure is increased, the value of TEP increases further in magnitude and near 7 GPa it becomes −50 μV/K. The pressure vs. resistance curve measured up to 30 GPa using diamond anvil (DAC)-based technique exhibits a broad hump near 12 GPa and exhibits hysteresis on pressure release. The ADXRD patterns up to 42 GPa show a gradual irreversible loss of long-range order in NiSi₂ with the diffraction lines progressively broadening under pressure. The FWHM of the diffraction lines show a rapid increase in the half-widths close to 0.5 GPa and also near 12 GPa. The computed band structure at a compression (without any disorder) corresponding to 12 GPa, exhibits an electronic topological transition (ETT). The rapid increase in disorder above 12 GPa implies that the ETT may be facilitating the structural disorder. It is suggested that the pressure drives the material through a region of entropic and energetic barriers and induces disorder in the material.     

百吉帕超高压下Ag的X光衍射实验和研究

 详细地介绍了百吉帕超高压实验的方法和步骤。实验是在具有杠杆式的金刚石对顶压砧（DAC）高压装置上完成的。以Ag为样品，进行百吉帕超高压下X光衍射的实验研究。最高压力达121 GPa，并获得了若干有意义的实验曲线和结果。     

Melting of B12P2 boron subphosphide under pressure

Melting of boron subphosphide (B₁₂P₂) to 26?GPa has been studied by in situ synchrotron X-ray powder diffraction in a laser-heated diamond anvil cell, and by quenching and electrical resistance measurements in a toroid-type high pressure apparatus. B₁₂P₂ melts congruently, and the melting curve has a positive slope of 23(6)?K/GPa. No solid-state phase transition was observed up to the melting in the whole pressure range under study.     

顽火辉石的高温高压同步辐射研究

 采用同步辐射能量色散X射线衍射技术、激光加热技术和金刚石对顶砧（DAC）高压装置,在温度为2 000 K和压力为23 GPa的范围内,对采自地幔二辉橄榄岩中的顽火斜方辉石,进行了原位的高温高压能量色散X射线衍射（EDXRD）测量。实验结果表明：当压力为15.3 GPa、温度为1 600 K时（相当于地球内部410 km处的地震波不连续界面的温压环境）,顽火斜方辉石转变为橄榄石的β相——瓦兹利石（Wadsleyite）相;继续加温加压至2 000 K、23 GPa时（相当于地球内部670 km处的地震波不连续界面的温压环境）,顽火斜方辉石相变为钛铁矿（Ilmenite）结构和钙钛矿（Perovskite）结构的混和相。实验结果进一步证明,在地幔中存在的两个地震波不连续界面是由橄榄石、顽火斜方辉石等矿物的相变引起的。     

环庚烷的高压拉曼光谱研究

 利用金刚石对顶砧（DAC）装置产生高压,在室温下对环庚烷进行了高压原位拉曼光谱研究。实验的最高压力是17.00 GPa。研究结果表明,在实验的压力范围内,室温常压下为液态的环庚烷在0.53 GPa发生了液-固相变;在3.45~5.58 GPa压力区间,环庚烷的拉曼频移随压力变化的曲线和拉曼峰的半高宽随压力的变化曲线都出现了拐点,由此判断,环庚烷可能发生了固-固相变。     

Static strength of gold compressed up to 127 GPa

Gold powder is compressed non-hydrostatically up to 127 GPa in a diamond anvil cell(DAC),and its angle dispersive X-ray diffraction patterns are recorded.The compressive strength of gold is investigated in a framework of the lattice strain theory by the line shift analysis.The result shows that the compressive strength of gold increases continuously with the pressure up to 106 GPa and reaches 2.8 GPa at the highest experimental pressure(127 GPa) achieved in our study.This result is in good agreement with our previous experimental result in a relevant pressure range.The compressive strength of gold may be the major source of the error in the equation-of-state measurement in various pressure environments.     

Magnetic transition of ferromagnetic material at high pressure using a novel system

A system for the investigation of the magnetic properties of materials under high pressure is fabricated based on diamond anvil cell （DAC） technology. The system is designed with an improved coil arranged around the diamond of a non-magnetic DAC. Using this system, the magnetic transition of ferromagnetic （Fe） sample under increasing pressure can be observed. We successfully obtain the evolution of magnetic properties as a function of applied pressure reaching 26.9 GPa in the Fe sample. A magnetic transition is observed at approximately 13 GPa, which is consistent with the theoretical prediction.     

Review: high pressure generation techniques beyond the limit of conventional diamond anvils

ABSTRACT

Current anvil designs and problems associated with various efforts to generate static high pressures beyond the limit of conventional diamond anvil cells (DACs) (～400?GPa) are reviewed. Pressures of up to 1?TPa have been reported by one research group using the double-stage DAC (ds-DAC) technique, but no other research group has successfully reproduced this high pressure result. Some research groups have used toroidal anvils, achieving pressures of >400?GPa. We have conducted numerous ds-DAC experiments and investigated the problems associated with such experiments. They include problems associated with various pressure scales in the multi-megabar region, difficulties in obtaining reliable X-ray diffraction patterns from micron-sized samples, and physical property measurements of tiny materials that may be harder than diamond. Each of these problems is discussed, following the summary of various experiments.     

β-BaB2O4晶体高压相变的X光衍射研究

 我们用金刚石压砧装置（DAC）高压X射线粉末衍射照相方法，研究了β-BaB₂O₄晶体的相变。压力从0.1 MPa逐步加至17.6 GPa，发现BBO由室温下的六方相经历了若干次相变后，当压力加至11.5 GPa时，转变为无定形相。在11.5 GPa压力前的相变是可逆的，一旦进入无定形相，则相变是不可逆的。     

ZnO纳米线在压力下的电学性质

 在金刚石压砧上测量了ZnO纳米线R-p和C-p关系,并和原先测量的纳米晶及体相ZnO的结果进行了比较。研究结果表明,ZnO纳米线在5.0 GPa左右发生相转变。其间的电阻-压力曲线呈指数下降趋势,电容呈指数上升趋势;在相转变之后电阻迅速上升,电容急速下降（指数下降）,这与一般的块状和纳米晶的相转变都有所不同,表现出了纳米线与非线状纳米晶的差别。     

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     

Neutron diffraction experiments in diamond and sapphire anvil cells

Diamond anvil cells (DAC) provide the highest static pressures ≥1?Mbar. Because of the low intensity of neutron sources, for a long time it was thought impossible to use DAC or other anvil cells in neutron experiments. We describe pressure cells with diamond and sapphire anvils and neutron instrumentation allowing neutron diffraction experiments to be carried out under pressures as high as 50?GPa, temperatures down to 0.1?K, and applied magnetic fields up to 7.5?T.     

Effect of pressure on electrical properties of SnS x Se1−x single crystals

The single crystals of tin monosulphoselenides in the form of a series SnS _x Se_1?x (where x?=?0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8?GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.