Mechanisms of Heat Transfer and Temperature Dependence of the Thermal Resistance of CaLa2S4 Crystals

Physics of the Solid State - The temperature dependence of the thermal resistance of CaLa2S4 crystals has been studied in the temperature range of 80–450 K based on the results of measuring...     

The Debye temperature and Grüneisen parameter of the CaLa<Subscript>2</Subscript>S<Subscript>4</Subscript>-La<Subscript>2</Subscript>S<Subscript>3</Subscript> system

The thermal expansion coefficient of solid solutions in the CaLa₂S₄-La₂S₃ system at a temperature of 300 K is investigated experimentally. The Debye temperature, the Grüneisen parameter, and the isothermal compressibility coefficient of solid solutions in the system under investigation are determined from the experimental thermal expansion coefficient. It is demonstrated that, upon substitution of calcium ions for cation vacancies in La₂S₃, the Debye temperature decreases, the isothermal compressibility coefficient increases, and the Grüneisen parameter remains constant for all compositions in the CaLa₂S₄-La₂S₃ system. A correlation between the ionic radii of Ca²⁺ and La³⁺, the concentration of cation vacancies, and the rigidity of the lattice, on the one hand, and the Debye temperature, the Grüneisen parameter, and the isothermal compressibility coefficient, on the other, is revealed for the studied samples.     

Temperature and pressure dependences of the thermal conductivity of As2(Se1-xTex)3 solid solutions

The effect of temperature and pressure on the thermal conductivity of solid solutions based on the As₂(Se_{1 - x}Te_x)₃ system was investigated in glassy and polycrystalline samples at 273–450 K and hydrostatic pressures of up to 0.35 GPa. The compound As₂Se₃ was studied in a temperature range of 300–760 K. Analysis showed that the short-cange order structure in As₂Se₃ remains unchanged upon the glass—liquid transition right up to 760 K.     

Temperature and concentration dependences of thermal conductivity of solid solutions of gadolinium and dysprosium sulfides

Thermal conductivity of a number of solid solutions of gadolinium and dysprosium sulfides has been studied experimentally within the temperature range 80-400 K. The work offers the data on thermal conductivity coefficient and lattice thermal conductivity of the studied samples. It was found that replacement of gadolinium ions by dysprosium ions leads to significant decrease of the samples?? thermal conductivity and changes its temperature dependence character due to the resonance scattering of phonons by paramagnetic ions of dysprosium. Influence of this mechanism of phonon scattering conditions the area of anomalous change observed on the concentration dependence of thermal conductivity coefficient.     

Thermal conductivity of polycrystalline zinc selenide

The thermal conductivity of optically transparent zinc selenide polycrystals fabricated by vapor deposition was experimentally studied in the temperature range 80–400 K in the as-deposited state and after deformation along the crystal growth direction followed by recrystallization. In the low-temperature range, textured ZnSe samples exhibit anisotropy of the thermal conductivity, which also persisted after their deformation and recrystallization. The anisotropy of the thermal conductivity is caused by phonon scattering by dislocations oriented along the crystal growth direction. The thermal conductivity of ZnSe at T>270 K is shown to be limited by the scattering of acoustic phonons by optical phonons.     

Heat conductivity of Gd2S3 with excess gadolinium

An experimental study of the heat conductivity of Gd₂S₃ with excess Gd content has been carried out in the temperature range from 80 to 400 K. It is shown that, as the concentration of excess Gd increases, the heat conductivity of the samples initially drops sharply to reach a minimum at ～0.25 at.% Gd, after which it increases only slightly. The reasons for such an anomalous variation of the heat conductivity of Gd₂S₃ with composition are discussed. The temperature dependence of the thermal resistance of the samples displays breaks characteristic of structural transformations in the temperature range 170–185 K.     

Heat conductivity of polycrystalline ZnS under uniform compression

The heat conductivity of polycrystalline zinc sulfide is investigated under hydrostatic pressure up to 0.35 GPa in the temperature range 273–420 K. It is found that an increase in the uniform pressure leads to an increase in the heat conductivity coefficient of ZnS. The Bridgman parameter characterizing the volume dependence of the heat conductivity is determined experimentally. A correlation between the heat conductivity coefficient under uniform compression and the evolution of the phonon spectrum is established.     

The effect of temperature and pressure on the heat conductivity of TlSbC<Stack><Subscript>2</Subscript><Superscript>VI</Superscript></Stack> (<Emphasis Type="Italic">C</Emphasis><Superscript>VI</Superscript> → S,Se, Te)

The effect of temperature and pressure on heat conductivity of ternary compounds TiSbC ₂^VI (C ^VI → S, Se, Te) in the solid and liquid states in a temperature range of 300–800 K, as well as under the pressure up to 0.35 GPa in a temperature range of 275–450 K, is studied. The dependence of heat conductivity on average atomic weight under the S → Se → Te transition is found. Analysis of the experimental data makes it possible to attribute TlSbS₂ to the class of substances exhibiting semiconductor-semiconductor melting behavior.     

The influence of structural features on the thermal conductivity of polycrystalline zinc sulfide

The thermal conductivity of single-crystal zinc sulfide and optically transparent zinc sulfide polycrystals differing in crystal grain size and density is experimentally investigated in the temperature range 80–400 K. It is shown that the thermal conductivity of polycrystalline samples substantially depends on the crystal grain size and the defect concentration in the grain-boundary layers. In zinc sulfide samples with a grain size of 1 μm, excess thermal resistance due to phonon scattering by grain boundaries is observed at temperatures T<130 K. It is demonstrated that, at higher temperatures (T>210 K), the heat transfer is associated not only with transverse phonon modes but also with longitudinal phonon modes and the role of the latter modes increases with an increase in temperature. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 2, 2002, pp. 251–256. Original Russian Text Copyright ? 2002 by Lugueva, Luguev.