Electrical properties of molybdenite single crystals

Molybdenite crystals used in the present work were grown by direct vapour transport or sublimation method. The electrical resistivities and I-V characteristics were measured at different temperatures in the symmetry plane. The room temperature resistance of a specimen annealed for different periods has also been measured. These results are described and discussed.     

Uniaxial stress dependence of the dielectric properties of barium titanate single crystals

BaTiO₃ single crystals were grown by the melt-grown method. The effect of uniaxial pressure (0–1700 bar) on the dielectric properties of these crystals has been systematically studied. The external stress showed obvious effects on these properties. An increase in the difference between the Curie T_c and Curie–Weiss T₀ temperatures induced by the applied pressure is observed. This could be ascribed to the inducing of non-ferroelectric cubic islands in the tetragonal phase by the applied compressive stress. On the other hand, the pressure behavior of thermal hysteresis and the ??/?T vs. T plot strongly suggests that the phase transition changes to second-order type with increasing pressure. The Curie–Weiss constant obtained from a modified Curie–Weiss law strongly decreases with increasing pressure, suggesting that the mechanism of phase transition is going to order–disorder type. An increase in the difference between the Curie T_c and Burn's T_B temperatures with increasing pressure is observed. This could be ascribed to the narrowing of the temperature range on which the Curie–Weiss law is valid. In general, the obtained results are in good agreement with hydrostatic pressure data. Some kind of relaxation near T_c, which is strongly coupled with strain caused by applied compressive stress, is postulated.     

Mesomorphic properties of a bent-shaped liquid crystalline monomer

We have prepared a new bent-shaped monomer designed for main chain liquid crystalline polymers. The mesomorphic behaviour of the monomer was fully characterized by DSC, polarizing optical microscopy and electro-optical measurements. Based on X-ray analysis of the monomer, its structural properties were established and a possible molecular arrangement in the mesophases is proposed. A direct comparison of the material shows that an introduction of an isolated double bond can slightly modify the mesomorphic properties of the liquid crystalline monomer in comparison with the alkyl-chain analogous bent-shaped compound studied previously.     

Temperature-dependent optical properties of GaSe layered single crystals

Optical properties of GaSe single crystals have been investigated using temperature-dependent transmission and room temperature reflection measurements in the wavelength range of 380–1100 nm. The analysis of the absorption data at room temperature showed the existence of indirect transitions in the crystal with energy band gap of 1.98 eV. Temperature dependence of the transmission measurements revealed the shift of the absorption edge toward lower energy as temperature is increased from 10 to 280 K. The rate of change of the indirect band gap was found as γ = ?6.6 × 10^?4 eV/K from the analysis of experimental data under the light of theoretical relation giving the band gap energy as a function of temperature. The absolute zero value of the band gap energy and Debye temperature were calculated from the same analysis. The Wemple–DiDomenico single-effective-oscillator model applied to refractive index dispersion data was used to determine the oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index values.     

Magnetic properties of oxides and silicon single crystals

The magnetic properties of single crystals Si, SrTiO₃, LaAlO₃, MgO, and (La,Sr)(Al,Ta)O₃ were investigated systematically. Three origins of the magnetizations of these crystals, namely, an intrinsic diamagnetic, a paramagnetic, and a ferromagnetic contribution, have been found to influence the magnetic signals measured on the crystals, in some important application scenarios such crystals being served as substrates with the magnetic thin film epitaxially grown on. Quantitative analyses methodologies were developed and thorough investigations were performed on the crystals with the intrinsic materials parameters thus revealed, especially that the intrinsic diamagnetic susceptibility differential dχ_dia/dT were identified quantitatively for the first time in SrTiO₃, LaAlO₃, MgO, and (La,Sr)(Al,Ta)O₃. The paramagnetic contribution is found to be the key in terms of the magnetic properties of the crystals, which in turn is in fact a consequence of the 3d impurities doping inside the crystal. All the intrinsic materials parameters are given in this paper as datasets, the datasets are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00028.     

单空位缺陷对石墨纳米带电子结构和输运性质的影响

基于第一性原理电子结构和输运性质计算,研究了单空位缺陷对单层石墨纳米带(包括zigzag型和armchair型带)电子性质的影响.研究发现,单空位缺陷使石墨纳米带在费米面上出现一平直的缺陷态能带;单空位缺陷的引入使zigzag型半导体性的石墨纳米带变为金属性,这在能带工程中有重要的应用价值;奇数宽度的armchair型石墨纳米带表现出金属特性,有着很好的导电性能,同时,偶数宽度的armchair型石墨带虽有金属性的能带结构,但却有类似半导体的伏安特性;单空位缺陷使得奇数宽度的armchair石墨纳米带导电 关键词： 石墨纳米带 单空位缺陷 电子结构 输运性质     

离子注入金红石单晶生成的金属Ni纳米晶的磁学性能研究

研究了能量为64keV、注量1×1017cm-2的Ni离子注入金红石TiO2单晶制备的植入金属纳米晶的微观结构和磁学性能。注入层的结构和磁学性能采用透射电子显微分析（TEM）和超导量子干涉磁强计（SQUID）进行分析。结果表明,金红石单晶中有尺寸为3～18nm的金属Ni纳米晶生成,注入区域基体明显非晶化。10K温度下金属Ni纳米晶的矫顽力约为16.8kA·m-1,比Ni块材的矫顽力大。样品的零场冷却/有场冷却（ZFC/FC）曲线表明,金属Ni纳米晶的截止温度约为85K。     

离子注入金红石单晶生成的金属Ni纳米晶的磁学性能研究

 研究了能量为64keV、注量1×10¹⁷cm^-2的Ni离子注入金红石TiO₂单晶制备的植入金属纳米晶的微观结构和磁学性能。注入层的结构和磁学性能采用透射电子显微分析（TEM）和超导量子干涉磁强计（SQUID）进行分析。结果表明，金红石单晶中有尺寸为3～18nm的金属Ni纳米晶生成，注入区域基体明显非晶化。10K温度下金属Ni纳米晶的矫顽力约为16.8kA·m^-1，比Ni块材的矫顽力大。样品的零场冷却/有场冷却（ZFC/FC）曲线表明，金属Ni纳米晶的截止温度约为85K。     

Single crystal growth,structural and transport properties of bad metal RhSb_2

We have successfully grown an arsenopyrite marcasite type RhSb2 single crystal, and systematically investigated its crystal structure, electrical transport, magnetic susceptibility, heat capacity, and thermodynamic properties. We found that the temperature-dependent resistivity exhibits a bad metal behavior with a board peak around 200 K. The magnetic susceptibility of RhSb2 shows diamagnetism from 300 K to 2 K. The low-temperature specific heat shows a metallic behavior with a quite small electronic specific-heat coefficient. No phase transition is observed in both specific heat and magnetic susceptibility data. The Hall resistivity measurements show that the conduction carriers are dominated by electrons with ne = 8.62 × 10¹⁸ cm^-3 at 2 K, and the electron carrier density increases rapidly above 200 K without change sign. Combining with ab-initio band structure calculations, we showed that the unusual peak around 200 K in resistivity is related to the distinct electronic structure of RhSb_2. In addition, a large thermopower S(T) about -140 μV/K is observed around 200 K, which might be useful for future thermoelectric applications.     

Space-charge-limited currents and photoconductive properties of Tl2InGaSe4 layered crystals

The extrinsic electronic parameters of Tl₂InGaSe₄ layered crystals were investigated through measurement of the temperature-dependent dark conductivity, space-charge-limited currents and photoconductivity. Analysis of the dark conductivity reveals the existence of two extrinsic energy levels at 0.40 and 0.51 eV below the conduction band edge, which are dominant above and below 260 K, respectively. Current–voltage characteristics show that the one at 0.51 eV is a trapping energy level with a concentration of (4.8–7.7) × 10¹⁰ cm^?3. Photoconductivity measurements reveal the existence of another energy level located at 0.16 eV. In the studied temperature range, the photocurrent increases with increasing temperature. The dependence of the photoconductivity on the incident light intensity exhibits a linear recombination character near room temperature and a supralinear character as the temperature decreases. The change in recombination mechanism is attributed to an exchange in the behavior of sensitizing and recombination centres.     

拓扑半金属材料的单晶生长研究进展

拓扑半金属已经成为凝聚态物理研究的一个热点领域,这类材料的单晶生长是研究其物理性质的基础.目前,对于拓扑材料的研究已经形成了以理论计算为指引,对潜在的拓扑材料进行单晶制备,并结合物性测量对理论预言加以验证的科研合作方式.在这种科研团队合作中,单晶生长起衔接作用.本文介绍了近年来拓扑半金属材料单晶生长方法,涵盖了拓扑Dirac半金属、Weyl半金属、Node-Line半金属以及其他打破常规分类的拓扑绝缘体及拓扑半金属材料等,并针对各个材料,详细总结了其生长方法.     

Effect of pressure on optical and electrical properties of tungsten diselenide single crystals

Optical absorption spectra of tungsten diselenide (WSe₂) single crystals subjected to different values of pressure (0, 2, 4 and 6 GPa) were obtained in the spectral range 700–1450 nm with the help of a UV–VIS–NIR spectrophotometer. The spectra were thoroughly analyzed in the absorption edge region for obtaining direct as well as indirect band gaps in this material. The high temperature resistivity and thermoelectric power on WSe₂ single crystals at various pressures were also studied. The results and their implications are discussed in the article.     

Physical properties of 8OS5 thioester studied by complementary methods

ABSTRACT

Properties of 4-n-pentylphenyl-4’-n-octyloxythiobenzoate (8OS5), belonging to the nOS5 homologous series, have been studied by complementary methods. The phase sequence, the phase transition temperatures, the thickness of molecular layers, the average distance between long axes of molecules and the correlation length were determined during cooling and heating. For the first time, simultaneous X-ray diffraction and differential scanning calorimetry measurements have been used to study mesomorphic properties. The results are compared with the ones obtained in standard measurements by means of differential scanning calorimetry, X-ray diffraction and polarizing optical microscopy. Meaning of experimental procedures applied in investigations of monotropic mesophases below a melting point is discussed.     

Electro-optic properties of nematic and ferroelectric liquid crystalline nanocolloids doped with partially reduced graphene oxide

Flakes of partially reduced graphene oxide (PRGO) were doped in nematic liquid crystals (NLCs) and ferroelectric liquid crystals (FLCs), respectively. The dielectric and electro-optical properties of NLCs doped with those flakes have been investigated. Threshold voltage and switching times are reduced by 30%–50%. This is primarily due to the decrease of the elastic properties of the nanocolloids compared to the non-doped nematics. The influence of the PRGO flakes on the spontaneous polarization, tilt angle and switching time of FLCs was investigated too. Such flakes reduce the response time by 40%–60%, increases spontaneous polarization by 20%–25% and increase the tilt angle by 15%–20%.     

Lateral IBIC characterization of single crystal synthetic diamond detectors

In order to evaluate the charge collection efficiency (CCE) profile of single‐crystal diamond devices based on a p‐type/intrinsic/metal configuration, a lateral Ion Beam Induced Charge (IBIC) analysis was performed over their cleaved cross sections using a 2 MeV proton microbeam. CCE profiles in the depth direction were extracted from the cross‐sectional maps at variable bias voltage. IBIC spectra relevant to the depletion region extending beneath the frontal Schottky electrode show a 100% CCE, with a spectral resolution of about 1.5%. The dependence of the width of the high efficiency region from applied bias voltage allows the constant residual doping concentration of the active region to be evaluated. The region where the electric field is absent shows an exponentially decreasing CCE profile, from which it is possible to estimate the diffusion length of the minority carriers by means of a drift–diffusion model. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Physical properties of hexagonal WN_2 under pressure

A first-principles study on the mechanical stability, elastic and thermodynamic properties of WN₂ with P63/mmc and P-6m2 phases are reported using the pseudo potential plane wave method within the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible WN₂ are determined in the wide pressure range. By the elastic stability criteria, it is predicted that P6₃/mmc and P-6m2 phases in WN₂ are not stable above 175.1 GPa and 170.1 GPa, respectively. Finally, by using the quasiharmonic Debye model, the isothermal and adiabatic bulk modulus, and the heat capacity of WN₂ are also successfully obtained.     

双温度氩-氮等离子体热力学和输运性质计算

获得覆盖较宽温度和压力范围内的等离子体热力学和输运性质是开展等离子体传热和流动过程数值模拟的必要条件.本文通过联立Saha方程、道尔顿分压定律以及电荷准中性条件求解等离子体组分;采用理想气体动力学理论计算等离子体热力学性质;基于Chapman-Enskog方法求解等离子体输运性质.利用上述方法计算了压力为0.1, 1.0和10.0 atm (1 atm=101325 Pa),电子温度在300—30000 K范围内,非局域热力学平衡(电子温度不等于重粒子温度)条件下氩-氮等离子体的热力学和输运性质.结果表明压力和非平衡度会影响等离子体中各化学反应过程,从而对氩-氮等离子体的热力学及输运性质有较大的影响.在局域热力学平衡条件下,计算获得的氩-氮等离子体输运性质和文献报道的数据符合良好.