The structures and thermoelectric properties of the infinitely adaptive series (Bi2)m(Bi2Te3)n

TL;DR

This paper investigates the structures and thermoelectric properties of the (Bi2)m(Bi2Te3)n homologous series, revealing their infinitely adaptive structures and varying thermopower, with implications for thermoelectric material design.

Contribution

It provides a unified structural description of the series and reports new thermoelectric property data, including doping effects, for multiple members of the series.

Findings

Bi2Te3 exhibits n-type thermopower; Bi-rich phases show p-type behavior.

Bi metal has the highest thermoelectric power factor among studied samples.

Doping with Sb and Se modifies the thermoelectric properties of Bi2Te.

Abstract

The structures and thermoelectric properties of the (Bi2)m(Bi2Te3)n homologous series, derived from stacking hexagonal Bi2 and Bi2Te3 blocks, are reported. The end-members of this series are metallic Bi and semiconducting Bi2Te3; nine members of the series have been studied. The structures form an infinitely adaptive series and a unified structural description based on a modulated structure approach is presented. The as-synthesized samples have thermopowers (S) that vary from n-type for Bi2Te3 to p-type for phases rich in Bi2 blocks but with some Bi2Te3 blocks present, to n-type again for Bi metal. The thermoelectric power factor (S2/rho) is highest for Bi metal (43 muW/K2 cm at 130 K), followed by Bi2Te3 (20 muW/K2 cm at 270 K), while Bi2Te (m:n = 5:2) and Bi7Te3 (m:n = 15:6) have 9 muW/K2 cm (at 240 K) and 11 muW/K2 (at 270 K), respectively. The results of doping studies with Sb and Se into Bi2Te are reported.