Crystal chemistry and superconductivity of pressure-induced phases in the In-Te system

Abstract

In the In-Te system, a pressure-induced Nad-type phase exists in the region In_0.80Te to In_1.5Te. Superconductivity exists in the whole range, with the maximum transition temperature occurring for the stoichiometric InTe. A hypothesis previously given for the metallic behavior of this phase and the decrease of transition temperature on either side of the stoichiometric InTe is further elaborated. It is proposed that the transformation to the NaCl-type structure removes the structural constraint on electron transfer existing in the normal InTe. A method for calculating carrier concentration is given and it is shown that the superconducting transition temperature is a function of carrier concentration. At least two other pressure-induced In-Te phases exist. One is In₃Te₄ which becomes superconducting at 1·25–1·15°K. In3Te4 has the anri-Sn₄As₃ structure with seven atoms in a rhombohedral unit cell, all lying on the threefold axis. The positional parameters of the atoms and interatomic distances are given and the coordination shown to be related to that found in the NaCl-type structure. Pressure-temperature experiments on normal In₂Te₃ indicate that a pressureinduced phase with this (or approximately this) composition cannot be obtained metastably without the presence of the In₃Te₄ and an unidentified phase. The pressure-induced In₂Te₃ phase has the well-known Bi₂Te₃ structure and is closely related to the In3Te4 structure. Superconductivity tests and X-ray diffraction investigation lead to the conclusion that the In3Te4 phases occurring with the In₂Te₃ phase are sometimes not stoichiometric and in such cases usually contain excess tellurium.