Structurally disordered In2Te3 semiconductor: novel insights

Abstract

The crystal structures of low- (α) and high-temperature (β) modifications of In₂Te₃ are refined for the first time. They crystallize with unique noncentrosymmetric face-centered cubic and half-Heusler arrangements, respectively. Both models are related with each other via a group–subgroup formalism. The small changes in unit-cell volume and entropy at the α → β structural phase transition indicate that it is of 2nd order. The strong structural disorder in α-In₂Te₃ results in a temperature-dependent behavior of the electrical resistivity similar to that of doped semiconductors (with a well-defined maximum) and extremely low thermal conductivity [κ(T) ≤ 0.7 W m⁻¹ K⁻¹]. Additional reasons for the poor electrical and thermal transport are low charge-carrier concentration and mobility, as well as enhanced phonon scattering at point defects, together with the presence of four-phonon processes and a ‘rattling’ effect. α-In₂Te₃ is found to be an n-type indirect semiconductor with an energy gap of 1.03 eV. All these physical characteristics are intrinsic properties of a high-quality stoichiometric crystal.