Thermal conductivity of materials with complex crystal structure
A.F.Ioffe Physico-technical Institute, Polytekhnicheskaya ul.26, St.Petersburg,194021, Russia
Thermal conductivity of crystal lattice is very important factor of thermoelectric figure of merit. Thermal conductivity of usual crystals with small number of atoms in unit cell is studied very well. There are many works on thermal conductivity of amorphous materials and material of very complex crystal lattice such as clathrates. This paper proposes an analysis of thermal conductivity of crystals of intermediate structures such as higher silicides, borides and compounds of Ag8SnSe6-type. The main feature of analyzed materials is a possibility to change the number of atoms in unit cell without changing the character of chemical bonds. A peculiarity of the majority of these materials is the crystal-like temperature dependence of thermal conductivity at low temperature and amorphous-like dependence at high temperature. The influence of unit cell mass, optical phonons contribution in the heat transfer and amorphization of phonon branches on absolute value and temperature dependence of thermal conductivity is analysed. A peculiarity of the majority of these materials is the crystal-like temperature dependence of thermal conductivity at low temperature and amorphous-like dependence at high temperature. The temperature of the change of the dependency type is connected with Debye temperature. The analysis made could be useful in a new thermoelectric search.