Properties of the superconducting state in molecular metallic hydrogen under pressure at 347 GPa

The thermodynamic properties of the superconducting state induced in metallic molecular hydrogen under the influence of pressure 347 GPa were determined. In particular, it has been shown that the critical temperature (T_C) changes in the range from 120 to 90 K for μ^?∈〈0.08,0.15〉, where μ^? is the value of the Coulomb pseudopotential. Next, the energy gap near the temperature of zero Kelvin (2Δ(0)) was calculated. It has been stated, that the dimensionless ratio 2Δ(0)/k_BT_C slightly decreases with the increase of μ^? from 3.98 to 3.84. In the last step, the ratio of effective electron mass (m^?_e) to the bare electron mass (m_e)) was determined. It has been proved that m^?_e/m_e takes its highest value equal to 1.96 for T=T_C.     

Thermodynamic properties of the superconducting state in YC2

We characterise the superconducting state of the binary carbide YC₂ by means of magnetisation and specific heat measurements. The thermodynamic properties reveal weak coupling superconductivity close to the type I limit (κ_GL ≈ 0.8). The specific heat data in the superconducting state, as well as the¹²C/¹³C-isotope shift are in excellent agreement with weak coupling BCS predictions.     

Thermoelectric and galvanomagnetic investigations of VI group semiconductors Se and Te at high pressure up to 30 GPa

At ultrahigh pressures up to 30 GPa the thermomagnetic Nernst–Ettingshausen effect was measured for Te and Se samples in the vicinity of semiconductor–metal phase boundary. The significant longitudinal and transverse Nernst–Ettingshausen effects observed for both semiconductors allowed one to estimate the scattering parameter for charge carriers. The increase in hole mobility obtained from longitudinal and transverse Nernst–Ettingshausen effects being consistent with the growth of magnetoresistance under pressure gave confirmation to the decrease in the effective mass of holes at the closure of direct semiconductor gap.     

低温高压液态空气储能系统分析

压缩空气储能是一种极具潜力的大规模储能技术,传统的压缩空气储能技术存在储能密度低、储存容积大等缺点,应用推广受到很大限制。液态空气储能技术是一种新兴的压缩空气储能技术,相比于传统压缩空气储能技术,能量储存密度显著提高。因此,基于低温空气液化原理,提出一种液态空气储能系统,其核心热力学过程为将空气降温液化后以高压状态存储,通过节流后的空气实现冷量回收,使得系统不需引入额外冷量。对该系统进行热力学分析和参数优化,结果表明系统效率可达50%以上。     

Raman and infrared investigations at room temperature of the internal modes behaviour in solid nitromethane‐h3 and ‐d3 up to 45 GPa

Raman and infrared spectra of internal phonons in solid nitromethane‐h₃ and ‐d₃ were measured as a function of pressure in the range 0–40 GPa at room temperature. Experiments were performed in diamond anvil cells. The evolution of the splitting of the various modes in condition of nearly hydrostatic compression supports the maintenance of the P2₁2₁2₁ crystal structure until the material chemically transforms into an amorphous phase. The observed pressure‐induced shifts of vibrational wavenumbers are consistent with computations recently reported in the literature. Infrared and Raman spectroscopies deliver complementary information on the internal modes behaviour. The continuous evolution of the infrared band shapes suggests a weak molecular distortion during the compression process. The strong modifications that are observed in the Raman bands of the nitro group are attributed to polarization effects arising from a rearrangement of the molecules inside the unit cell in the pressure range 10–12 GPa, a consequence of a close intermolecular O…H approach. Copyright © 2007 John Wiley & Sons, Ltd.     

Structure of nanocrystalline ZnO up to 85 GPa

The structure of nanocrystalline and bulk polycrystalline ZnO were examined up to 85 GPa and 50 GPa, respectively using synchrotron X-rays and diamond anvil cells at ambient conditions. The transition from the wurtzite to the rock salt phase in the nano-ZnO takes place at 10.5 GPa; this transition pressure is 1.5 GPa higher than in bulk ZnO. A large volume collapse of about 17.5% is observed during the transition in both systems. The rocksalt phase is stable and no structural transitions are observed for both compounds at higher pressures up to the experimental limit. On decompression the rocksalt phase is found to co-exist with the wurtzite phase at ambient conditions for the nano-ZnO.     

Temperature of the superconducting transition in the TiV alloy at pressures up to 60.8 GPa

The dependence of the temperature of the transition to the superconducting state T _c on the pressure up to 60.8 GPa is measured for the TiV alloy. The dependence T _c (P) is increasing except for an anomaly in the form of a local minimum near P = 10 GPa. At the maximum pressure of 60.8 GPa, the superconducting transition temperature T _c reaches 18.2 K. The obtained curve T _c (P) is compared with the known dependences for pure vanadium, for which T _c (P) increases to 17.2 K at P = 120 GPa, and for pure niobium and the ZrNb alloy, for which the dependences T _c (P) also have anomalies in the form of local maxima at pressures of 5–10 GPa.     

Volume compression of thallium to 45 GPa

Abstract

High-pressure structural transition and volume compression for thallium were investigated to 45 GPa in a diamond anvil cell using the angular dispersive X-ray diffraction technique. Except for the known polymorphic transition at 3.7 GPa, no other structural change was observed in this pressure range. The equation of state of the high pressure phase has been obtained: its initial bulk modulus, B₀ = 33.1 GPa, is lower by 10% than that of the hexagonal phase at normal pressure.     

Equation of state of LiCoO_2 under 30 GPa pressure

LiCoO_2 is one of the most important cathode materials for high energy density lithium ion batteries. The compressed behavior of LiCoO_2 under high pressure has been investigated using synchrotron radiation x-ray diffraction. It is found that LiCoO_2 maintains hexagonal symmetry up to the maximum pressure of 30.1 GPa without phase transition. The elastic modulus at ambient pressure is 159.5(2.2) GPa and its first derivative is 3.92(0.23). In addition, the high-pressure compression behavior of LiCoO_2 has been studied by first principles calculations. The derived bulk modulus of LiCoO_2 is 141.6 GPa.     

In situ Raman spectroscopy of cubic boron nitride to 90 GPa and 800 K

The temperature and pressure dependences of the Raman spectrum of the transverse-optical mode of cubic boron nitride were calibrated for applications to a Raman spectroscopy pressure sensor in optical cells to about 800 K and 90 GPa. A significant deviation from linearity of the pressure dependence is confirmed at pressures above 20 GPa. At ambient temperature, dv/dP slopes are 3.41(7) and 2.04(7) cm⁻¹/GPa at 0 and 90 GPa, respectively. A polynomial expression is used to fit the pressure–temperature dependence of the Raman line. The pressure dependence does not significantly change with temperature, as determined from experiments conducted up to 800 K. At 0 GPa, the dv/dP slope is 3.46(7) cm⁻¹/GPa at 800 K. At pressures above 90 GPa, the Raman spectrum of the transverse-optical mode cannot be observed because of an overlap of the signals of cubic boron nitride and diamond used as the anvils in the high-pressure cell.     

Thermodynamic and transport properties of superconducting Mg10B2

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2/dT = 0.44 T/K at the transition temperature of Tc = 40.2 K. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of dHc/dT at Tc is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter kappa approximately 26. Estimates of the critical supercurrent density, Jc, using hysteresis loops and the Bean model, give critical current densities on the order of 10(5) A/cm2. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb3Sn.     

Crystallographic investigations and comparison of superconducting and nonsuperconducting CeCu2Si2

Two samples of CeCu _x Si₂ withx=1.8 (non superconducting) andx=2.2 (superconducting) have been investigated by neutron powder diffraction. Both samples were characterized crystallographically and then their impurity content and lattice site occupation were determined. Anisotropic thermal vibrations of the Cu and Si atoms is detected at low temperatures. A relationship between the structural parameterz (defining the distance Ce to Si) and the occurance of superconductivity is suggested.     

Thermodynamic properties of superconducting nuclear matter

Phase diagrams of superconducting nuclear matter are calculated by solving a set of finite temperature gap equations, using several Skyrme effective interactions. Our results indicate that nuclear matter may have a superconducting phase in a small region with density near one half of the normal nuclear matter density and temperature k_BT ≲ 1.4 MeV. Our calculation is based on a finite temperature Green's function method with an abnormal pair cutoff approximation. The same approximation is employed in deriving the internal energy, entropy and chemical potential of superconducting nuclear matter. In this way, its equation of state is obtained, and compared with that of normal nuclear matter. The energy gap of superconducting nuclear matter is found to depend rather sensitively on both density and temperature. This dependence is analysed in terms of the Skyrme interaction parameters. The correlation effect on chemical potential is found to be important at high density, and its inclusion is essential in determining the equation of state of superconducting nuclear matter.