A study on the electrical property of HgSe under high pressure

Using a microcircuit fabricated on a diamond anvil cell, we have measured in-situ conductivity of HgSe under high pressures, and investigated the temperature dependence of conductivity under several different pressures. The result shows that HgSe has a pressure-induced transition sequence from a semimetal to a semiconductor to a metal, similar to that in HgTe. Several discontinuous changes in conductivity are observed at around 1.5, 17, 29 and 49GPa, corresponding to the phase transitions from zinc-blende to cinnabar to rocksalt to orthorhombic to an unknown structure, respectively. In comparison with HgTe, it is speculated that the unknown structure may be a distorted CsCl structure. For the cinnabar-HgSe, the energy gap as a function of pressure is obtained according to the temperature dependence of conductivity. The plot of the temperature dependence of conductivity indicates that the unknown structure of HgSe has an electrical property of a conductor.     

Study of structural stabilities and optical properties of HgTe under high pressure

A theoretical investigation on the structural stabilities and electronic properties of HgTe under high pressure was conducted using first principles based on density functional theory. Our results demonstrate that the sequence of the pressure-induced phase transitions of HgTe is from the zinc blende, to cinnabar, rocksalt, orthorhombic, and CsCl-type structures. The pressure effects on the optical properties were discussed and compared with previous calculations and experimental data whenever available.     

Conductive phthalocyanines under very high pressure

Vanadyl, thorium, lead, copper, zinc and metal-free phthalocyanines become appreciably conductive under the static pressure of up to several hundred kilobars. The least resistivity observed is 0.1 $\text{Ω}$-cm for vanadyl phthalocyanine. There appear minima in the curves showing resistance change with pressure for vanadyl, thorium, lead and metal-free phthalocyanines.     

The electrical transportation and carrier behavior of ZnSe under high pressure

With in situ electrical resistivity and Hall effect measurement, electrical transportation property and charge carrier behavior of ZnSe were investigated under high pressure using a diamond anvil cell (DAC). The electrical resistivity changed discontinuously at 7.7 and 11.9?GPa, corresponding to the phase transitions of ZnSe. In the pressure interval of 7.7–11.9?GPa, the electrical resistivity changed continuously, indicating the existence of the intermediate phase between the zinc blende and rock salt phases. The difference of carrier characteristic between the intermediate and rock salt phases can also suggest the existence of the intermediate phase. For the intermediate phase, the increase in electrical resistivity is from the decrease in mobility. While for the rock salt phase, the increase in charge carrier concentration leads to the decrease in electrical resistivity.     

Structural stability and electrical properties of AIB2-type MnB2 under high pressureStructural stability and electrical properties of AIB2-type MnB2 under high pressureStructural stability and electrical properties of AIB2-type MnB2 under high pressureStructural stability and electrical properties of AIB2-type MnB2 under high pressure

The structural stability and electrical properties of A1B2-type MnB2 were studied based on high pressure angle- dispersive x-ray diffraction, in situ electrical resistivity measured in a diamond anvil cell （DAC） and first-principles calcu- lations under high pressure. The x-ray diffraction results show that the structure of A1B2-type MnB2 remains stable up to 42.6 GPa. From the equation of state of MnB2, we obtained a bulk modulus value of 169.9~3.7 GPa with a fixed pressure derivative of 4, which indicates that A1B2-type MnB2 is a hard and incompressible material. The electrical resistance un- dergoes a transition at about 19.3 GPa, which can be explained by a transition of manganese 3d electrons from localization to delocalization under high pressure.     

Acoustical measurements in solids under very high pressure

Two acoustical techniques to measure sound velocities in solids under high static pressure are examined from both theoretical and experimental points of view. The ultrasonic technique is suitable for measuring the elastic properties of solids under a pressure of a few gigapascals, whereas the Brillouin scattering technique is particularly useful for transparent materials under a few tens of gigapascals. We illustrate these acoustical methods by the study of the elastic behaviour of two perovskite crystals: RbCdF₃ and SrTiO₃.     

Life of Artemia under very high pressure

The experiment on the search for life under very high pressure done for small animal tardigrades has been extended to a plankton, Artemia. It was found that cysts, or dried eggs, of Artemia remain alive after being exposed to a very high hydrostatic pressure of 7.5 GPa for 42 h. We are convinced that at least two kinds of small animals are still alive after being exposed to such high hydrostatic pressure of 7.5 GPa, which corresponds to the pressure at the depth of about 180 km below the surface of the Earth, i.e., Mantle pressure. The results of the present investigation suggest the possibility that Artemia, as well as tardigrade may have traveled through outer space in a large meteorite, and reached the Earth alive from another planet or galaxy.     

Effects of annealing on the electrical properties of HgTe crystals

The carrier mobility of HgTe crystals at 15°C increased to as much as $\text{33,000}\text{cm}{}^2\text{V sec}$, and the transverse magnetoresistance decreased, when the crystals were annealed long enough in mercury vapor. The results are compared with our calculations of the galvanomagnetic effects for mixed scattering by phonons and charged centers, which was made for a parabolic band. It is concluded that the density of charged centers decreases with annealing, and that acoustic phonons may be the dominant scattering sources near room temperature.     

Structural and electrical transport properties of charge density wave material LaAgSb_2 under high pressure

Layered lanthanum silver antimonide LaAgSb_2 exhibits both charge density wave(CDW) order and Dirac-cone-like band structure at ambient pressure.Here,we systematically investigate the pressure evolution of structural and electronic properties of LaAgSb_2 single crystal.We show that the CDW order is destabilized under compression,as evidenced by the gradual suppression of magnetoresistance.At P_C～22 GPa,synchrotron x-ray diffraction and Raman scattering measurements reveal a structural modification at room-temperature.Meanwhile,the sign change of the Hall coefficient is observed at 5 K.Our results demonstrate the tunability of CDW order in the pressurized LaAgSb_2 single crystal,which can be helpful for its potential applications in the next-generation devices.     

Thermodynamic properties of OsB under high temperature and high pressure

The energy-volume curves of OsB have been obtained using the first-principles plane-wave ultrasoft-pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA) and local density approximation (LDA). Using the quasi-harmonic Debye model we first analyze the specific heat, the coefficients of thermal expansion as well as the thermodynamic Grüneisen parameter of OsB in a wide temperature range at high pressure. At temperature 300 K, the coefficients of thermal expansion α_V by LDA and GGA calculations are 1.67×10⁻⁵ 1/K and 2.01×10⁻⁵ 1/K, respectively. The specific heat of OsB at constant pressure (volume) is also calculated. Meanwhile, we find that the Debye temperature of OsB increases monotonically with increasing pressure. The present study leads to a better understanding of how the OsB materials respond to pressure and temperature.     

硼硫协同掺杂金刚石的高压合成与电学性能研究

FeNiMnCo-C体系中,在压力6.5 GPa、温度1280—1300℃的极端物理条件下,采用温度梯度法成功合成了硼(B)、硫(S)协同掺杂金刚石大单晶.通过傅里叶红外光谱测试对高温高压所制备金刚石中的杂质进行了表征.借助霍尔效应对典型金刚石样品的电输运性能进行了测试,测试结果表明:硼硫协同掺杂有利于提高p型金刚石的电导率,而且硼硫在合成体系中的添加比例可以决定金刚石的p, n特性.此外,第一性原理计算结果表明,合成体系中不同比例的硼硫协同掺杂对金刚石的p, n特性以及电导率有着直接的影响,计算结果与实验测试结果相吻合.     

高压下ZnSe直流和交流电学性质的研究

采用高压原位测量技术在0–35 GPa压力范围内对ZnSe直流和交流电学性质进行了研究. 通过分析直流电学测量结果可知,在实验压力区间内ZnSe经历了由纤锌矿转变为朱砂相再转变为岩盐相的两次相结构转变. 分析温度与材料电阻率的变化关系表明ZnSe在高压下的相变为金属化相变,并通过交流阻抗谱的测量实验证实了这个结论. 进一步比较低压条件下晶粒和晶界电阻的变化,表明朱砂相结构的ZnSe更接近各向同性材料. 关键词： 高压 ZnSe 电学     

Preserving life of moss Ptychomitrium under very high pressure

The experiment on the search for life under very high pressure done on small animal, tardigrade, has been extended to the moss Ptychomitrium. Several spore placentas of the moss Ptychomitrium were sealed in a small Teflon capsule together with fluorinate as liquid pressure medium. The capsule was put in the center of a pyrophillite cube. This cube was compressed by six tungsten-carbide second-stage anvils with a front edge length of 4.0 mm. These anvils were compressed by a first stage, 250 ton press. It was proven that 80-90% of the spores were alive and germinated after being exposed to the maximum pressure of 7.5 GPa for up to 48 h. Furthermore, a relatively high germination rate of about 35% was retained even after exposure to 7.5 GPa for 6 days. The pressure tolerance of moss is found to be much stronger than tardigrades.     

Elastic properties of nanocrystalline forsterite under high pressure and high temperature

A simple theoretical model is developed to study the pressure–volume–temperature relationship and applied for nanocrystalline forsterite in the temperature range 300–1573 K and pressure range 0–9.6 GPa. The results obtained with the present model are in quite close agreement to the experimental values. The model is therefore extended to study the variation of bulk modulus and the coefficient of volume thermal expansion under high pressure and high temperature. The present study also reveals that the quasi-harmonic approximation, i.e., the product of bulk modulus and the coefficient of volume thermal expansion as constant, is valid at least up to the temperature 1573 K and pressure 9.6 GPa in case of nanocrystalline forsterite.     

Structural and elastic properties of TiN under high pressure

We have investigated the structural and elastic properties of TiN at high pressures by the first-principles plane wave pseudopotential density functional theory method at applied pressures up to 45.4 GPa. The obtained normalized volume dependence of the resulting pressure is in excellent agreement with the experimental data investigated using synchrotron radial x-ray diffraction (RXRD) under nonhydrostatic compression up to 45.4 GPa in a diamond-anvil cell. Three independent elastic constants at zero pressure and high pressure are calculated. From the obtained elastic constants, the bulk modulus, Young's modulus, shear modulus, acoustic velocity and Debye temperature as a function of the applied pressure are also successfully obtained.     

Thermodynamic and transport properties of SmS under high pressure

We measured transport and thermodynamic properties of the valence-fluctuating phase of SmS up to 8.5 kbar, and found a bump structure in the temperature dependence of the electrical resistivity and a Schottky-type anomaly in the temperature dependence of the thermal expansion coefficient at a characteristic temperature T₀. We also observed that the absolute value of the Hall constant rapidly increases below T₀. From these results, we argue that the steep rise of the electrical resistivity below T₀ is inherent to golden SmS and can be ascribed to the decrease in the carrier concentration possibly due to the pseudo gap formation.     

Metal-insulator transition in a HgTe quantum well under hydrostatic pressure

The 2D semimetal in a 20 nm (100) HgTe quantum well is characterized by a comparatively low overlap between the conduction and the valence bands induced by lattice mismatch. In the present paper we report the results of transport measurements in this quantum well under hydrostatic pressure of 14.4 kbar. By applying pressure we have further reduced the band overlap, thereby creating favorable conditions for the formation of the excitonic insulator state. As a result, we observed that the metallic-like temperature dependence of the conductivity at lowering temperature sharply changes to the activated behavior, signaling the onset of an excitonic insulator regime.