Defect structure influence on thermal conductivity of gadolinium sulfides

S. Luguev1, N. Lugueva1, V. Sokolov2 and T. Luguev1

1Institute of Physics of Daghestan Scientific Center of RAS, Russia
2Nikolaev Institute of Inorganic Chemistry, Siberian Branch of RAS, Russia

Keywords: defect structure
property: thermal conductivity
material: gadolinium sulfides

Crystallizing in the structure of Th3P4-type gadolinium sulfides GdSx form the solid solutions with a homogeneity x range from 1.50 to 1.45. Within this range the structural type persists, the lattice parameter varies slightly, but there is a significant change in the number of cationic vacancies and carrier concentration. The possibility of regulating the concentration of stoichiometric vacancies and free carriers in these solid solutions allows significantly affects their thermal and electrical properties by changing the composition of the homogeneous phase. The present paper reports the results of experimental investigation of temperature and concentration dependences of the thermal conductivity coefficient of crystallized in the thorium phosphide type structure solid solutions GdSx in the range 80-400 K.

The investigations showed that with the composition change of the solid solution in system GdSx not only the value but also temperature dependence of the thermal conductivity change significantly. The experimental data analysis showed that the lattice, electronic and photonic components make the contribution to the heat transfer in these solid solutions. The change of lattice defects, concentration of free electrons and chemical bonding in crystals at the composition changing has the essential influence on these mechanisms. In all compositions the phonon heat transport is the dominant mechanism of heat transfer. With increasing of sulfur concentration in the solid solution the contribution of the electronic component in the thermal conductivity decreases and near GdS1.50, it is negligible. At temperatures above 200 K in GdS1.50 involvement in heat transfer of the photon component are observed. The role of phonon scattering by vacancies, impurities and electrons was determined in the crystals with different concentrations of defects and carriers. In samples with low concentrations of electrons the thermal conductivity temperature dependence has the form typical for the phonon heat conductivity and phonon-phonon and phonon-defect scattering processes. With increasing electron concentration in the samples the character of the temperature dependence of the thermal conductivity is more complicated due to the participation of free carriers in the heat transport and phonon scattering. The composition dependence of the GdSx system thermal conductivity has a complicated character which is determined by the change of phonon, electron and photon contributions into heat transfer, and also by the influence of the change of the electron concentration, lattice defects and chemical bond on these mechanisms.

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