Transport properties of conducting and semiconducting anisotropic mixtures

Abstract

The authors present thermoelectric power and thermal and electrical conductivity measurements on mixtures of conducting (WTe₂) and semiconducting (WSe₂) powders, characterised both by a geometrical anisotropy (grain shapes and sizes) and by a transport property anisotropy. Results are given as a function of the volume fraction of the conducting phase x. The measured anisotropies are not simply related to the material anisotropies because of twistedness of the current lines. The thermoelectric power of the samples is nearly isotropic. The thermal conductivity anisotropy presents a regular variation with x, whereas the electrical conductivity anisotropy has a minimum around a percolation threshold. Their results are interpreted using the percolation and effective medium models.