Formation Phases and Electrical Properties of Ge-Bi-Te Compounds with Homologous Structures

Abstract

We prepared polycrystalline samples of GeBi_6−x In _x Te₁₀ (x = 0, 0.06, 0.18, 0.3, and 0.6) by melting a stoichiometric mixture of Ge, Bi, In, and Te, followed by quenching in water and annealing at 723 K for 1 week. Under these preparation conditions and irrespective of the degree of In-substitution, the samples contained two different periodic structures: GeBi₆Te₁₀ and GeBi₄Te₇ structures. The relationship between the Seebeck coefficient, electrical resistivity, and phase fraction of the two structures was investigated at room temperature. We concluded that changes in the transport properties for all samples may reflect a mixture effect of the phase fraction of the two structures and the amounts of In-substitution in the framework of the assumed structure model in this study. The thermoelectric properties of the samples with x = 0 and 0.18 were determined from 300 K to 723 K from the measured electrical properties and the reported lattice thermal conductivity. The sample with x = 0.18 had the highest dimensionless figure of merit: ZT _max = 0.11 at 466 K, which was 1.8 times larger than that of the sample with x = 0.