Solid solutions of In 2Te 3 in Sb 2Te 3 and Bi 2Te 3

Abstract

Solid solutions of the compositions (Sb 2Te 3) 1− x (In 2Te 3) x , where x ⩽ 0.45, and (Bi 2Te 3) 1− x (In 2Te 3) x , where x ⩽ 0.25, have been prepared in mono- or oligo-crystalline form by directional freezing. The crystals retain the hexagonal structure characteristic of Sb 2Te 3 and Bi 2Te 3, but in both cases the volume of the unit cell diminishes with increasing In concentration (measured spectrochemically). Density measurements and phase analysis prove that the mechanism of solid solution is either the direct replacement of Sb (or Bi) by In or the simultaneous replacement of Te by In and Sb (or Bi) by Te. The resistivity, Hall coefficient, and Seebeck coefficient have been measured. The In-substituted Sb 2Te 3 solutions are always p-type, but an inversion to n-type conductivity occurs in the Bi 2Te 3 alloys, particularly at high In concentrations. The magnitude of the Hall coefficient is virtually unchanged by the introduction of In. In the Bi 2Te 3 alloys, the carrier mobility is not strongly dependent on In content, but in the Sb 2Te 3 alloys it decreases sharply with increasing In concentration. The magnetic susceptibility is unchanged by the introduction of In. On the basis of these results, a model is proposed in which the nonbonding s-orbital of an In atom is transformed in the crystal into new states in the conduction band. Information is appended on the phase diagram of the In-Sb-Te ternary system.