Effect of Sb doping on CVT grown SnTe single crystals electrical and thermal properties

Journal of Materials Science: Materials in Electronics - Pure and Sb-doped SnTe single crystals are grown by chemical vapour transport (CVT) technique. Doping of 5%, 10%, and 15% Sb is done in...     

On the anisotropic thermal conductivity of shape memory alloy single crystals

Summary This paper addresses the issue of anisotropy in overall thermal conductivity of a shape memory alloy microstructure that is single crystalline in the high temperature austenitic state. The Voigt and Reuss bounds of the thermal conductivity are given. It is shown that the trace of the Voigt bound is independent of the specific variants that may exist and their orientations in the microstructure, whereas it is not so for the Reuss bound. It is also shown that both bounds of a purely self-accomodated martensitic microstructure originating from a cubic parent phase are isotropic and independent of the geometric properties of the variants. The bounds are then applied to the study of orthorhombic martensitic SMAs that are single crystalline in the cubic austenitic state. Using the resolved shear stress approach for variant selection, the impact of anisotropy in the thermal conductivity components of the orthorhombic martensite is studied for a single variant microstructure where the Voigt and Reuss bounds are used as estimates for the thermal conductivity of a cylindrical domain. Their impact on the normalized average steady state temperature and the normalized time taken to attain steady state are studied. This work is the precursor of experimental research on the anisotropy in thermal conductivity of shape memory alloys, of which virtually none exists in the open literature today.     

Effect of rare-earth doping on the electrical properties of InSe single crystals

The effect of rare-earth doping (R = Gd, Dy, Ho) to different levels (0, 10^?5, 10^?4, 10^?3, 10^?2, and 10^?1 at %) on threshold switching and low-frequency current oscillations in single crystals of indium selenide, a layered III–VI semiconductor, has been studied in broad ranges of temperatures (77–400 K), wavelengths (0.30–3.50 μm), and illuminances (up to ～10² lx). The results are interpreted in terms of the anisotropic chemical bonding in n-InSe and its response to rare-earth doping.     

Lattice thermal conductivity of bismuth-antimony alloy single crystals at low temperatures

Thermal conductivity measurements in a number of bismuth-antimony alloy single crystals, with antimony concentrations from 1.72 at.% to 20 at.% are reported. Analysis of the results shows that in this alloy system, below about 25 K, the heat carriers are predominantly phonons. Callaway's theoretical model for lattice thermal conductivity has been utilized for the analysis of the results, using various phonon-scattering processes, and this model has been found to give a good fit to the experimental data, particularly below 25 K, where lattice conduction predominates. The Casimir model for finding the characteristic length for boundary scattering fails to explain the experimental results. This indicates the existence of microscale fluctuations in the composition of the alloy.     

Influence of structural defects on the thermal conductivity of polycrystalline and single-crystal PbTe

We have measured the thermal conductivity of unannealed and annealed (800 K, 120 h) polycrystalline and single-crystal PbTe samples at temperatures from 80 to 303 K, evaluated the electronic and lattice components of their thermal conductivity, and determined the thermal resistivity due to structural defects, whose concentration in the unannealed single-crystal samples reaches ∼10¹⁷ cm⁻³. The results demonstrate that the thermal resistivity of the unannealed polycrystalline and single-crystal samples is 9.4 and 1.7 cm K/W, respectively. Annealing eliminates the defects, thereby increasing the lattice thermal conductivity of the material.     

Growing and polishing large thallium single crystals

An easily repeatable method has been developed for growing large hexagonal close-packed thallium single crystals, and obtaining specimens with high quality surfaces. Also a new polishing procedure for the (0001) surface is described, which results in a nearly optically flat crystal surface.     

Low-temperature anisotropy of thermal conductivity of tin single crystals doped with zinc

The thermal conductivity of tin single crystals with zinc admixtures has been measured in the temperature range 3.5–25 K for concentrations up to 0.1 wt%. The anisotropy of thermal conductivity for two orientations, [001] and [010], has been determined. It was found that the influence of zinc admixture on the thermal conductivity anisotropy is of a complex, temperature-dependent character.Nomenclature T ₁ T ₂ Temperature differences in the specimen - Thermal conductivity coefficient - W Thermal resistivity - A, B, C Constants in Eq. (1) - T Temperature - ^th Residual electrical resistivity calculated from W-F law - ₀ Residual electrical resistivity from measurements - L ₀ Lorenz constant - _th Anisotropy coefficient of thermal conductivity - _el Anisotropy coefficient of electrical conductivity - c Admixture concentration     

Investigation of the thermal conductivity of molecular crystals

The nonsteady-state heated-wire method was used to measure the coefficients of thermal conductivity of benzene and cyclohexene over the temperature range from–196°C to +30°C. We have attempted to explain the heat-transger mechanism in these substances.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 4, pp. 705–709, October, 1970.     

Effect of stoichiometry on the thermal expansion coefficients of lithium niobate single crystals

The chemical analysis of LiNbO₃ single crystals, with different melt compositions (Li/Nb) _m =0·945, 1·0, 1·1 and 1·2, grown by slow cooling technique, reveals a remarkable difference in solid and melt compositions. The thermal expansion coefficients alonga andc axes, determined by using Newton’s ring experiment, are found to increase anisotropically with increase in (Li/Nb) _m ratio. The variation in thermal expansion coefficient with increase in the (Li/Nb) _m ratio is discussed in the light of defect chemistry i.e. the partial replacement of Li⁺ by excess Nb⁵⁺ creates additional cation vacancies to attain the electro-neutrality in the crystal.     

Effect of amino acid doping on the growth and ferroelectric properties of triglycine sulphate single crystals

Effect of amino acids (l-leucine and isoleucine) doping on the growth aspects and ferroelectric properties of triglycine sulphate crystals has been studied. Pure and doped crystals were grown from aqueous solution by low temperature solution growth technique. The cell parameter values were found to significantly vary for doped crystals. Fourier transform infrared analysis confirmed the presence of functional groups in the grown crystal. Morphology study reveals that amino acid doping induces faster growth rate along b-direction leading to a wide b-plane and hence suitable for pyroelectric detector applications. Ferroelectric domain structure has been studied by atomic force microscopy and hysteresis measurements reveal an increase of coercive field due to the formation of single domain pattern.     

Cobalt diffusion during doping of ZnSe single crystals

Cobalt diffusion into single crystals of the compound semiconductor ZnSe has been studied under the conditions of the S _ZnSe-S _CoSe-L _Zn-V phase equilibrium at temperatures from 700 to 970°C, and the diffusion coefficients of cobalt in (100)-and (111)-oriented single-crystal samples of zinc selenide have been determined as functions of temperature. The diffusion rate of cobalt along the [111] direction is shown to exceed that along [100].     

Electrical conductivity of yttria-stabilized zirconia single crystals

The electrical conductivities of YSZ single crystals with various compositions covering FSZ and PSZ regions were measured by a complex impedance method and a four-probe a.c. method. The conductivities changed significantly as a function of composition. A simple conduction model for PSZ showed that the tetragonal phase is a good oxygen ionic conductor having an activation energy for motion of about 0.8 to 0.9 eV. It is promising for low temperature application of a solid state electrolyte.     

HCI气相掺杂对聚苯胺电导率影响规律的探讨

采用气相掺杂这种新的掺杂方法对低电导率的导电聚苯胺进行再掺杂,气相掺杂30min的聚苯胺的电导率约为未掺杂导电聚苯胺的4倍,并对其结构进行红外表征,探讨了电导率发生变化的内在机理。该法简便易操作,不引入杂质,不污染环境,是一种很有发展前景的新方法。     

Effect of thallium doping on the parameters of localized states in <Emphasis Type="Italic">p</Emphasis>-GaSe single crystals

Experimental evidence is presented that, at temperatures from 167 to 250 K, electrical transport in undoped and thallium-doped p-GaSe single crystals is due to variable-range hopping. The main parameters of localized states in the band gap of p-GaSe〈T1〉 (0, 1, 2, and 2.5 mol % Tl) have been estimated as functions of doping level.     

Effect of thermal coarsening on the thermal conductivity of nanoporous gold

The thermal conductivities of nanoporous gold (NPG) microwires annealed at different temperatures have been measured in the temperature range from 100 to 320 K. Considering the electron-surface scattering, the thermal conductivity is expected to increase with the increase of ligament diameter. However, the thermal conductivity of NPG microwire is found to decrease after thermal coarsening, and has a maximum value at around 250 K for the as-dealloyed sample. We suggest that the defects accumulating at a relatively high temperature and the reduction in defect spacing may cause these temperature behaviors of thermal conductivity. Taking into account the electron scattering on ligament surfaces and defects, a modified theoretical model for the thermal conductivity of nanoporous metal is proposed to agree with our experimental results.     

Indium doping of ZnSe single crystals during vapor phase growth

A process for indium doping of ZnSe single crystals during vapor phase growth is described. The solubility limit of indium in ZnSe is determined as a function of temperature and zinc selenide stoichiometry. The conclusion is drawn that the entire homogeneity range of ZnSe in the equilibrium phase diagram lies at selenium-enriched compositions.