Electrical and microstructural properties of Bi_2−x Sb _x Te and Bi_2−x Sb _x Te₂ foils obtained by the ultrarapid quenching process

Abstract

This paper is concerned with the feasibility and reproducibility of the ultrarapid quenching process used to fabricate Bi_2−x Sb _x Te and Bi_2−x Sb _x Te₂ alloys for thermoelectric applications. Microstructural properties of the materials, obtained in the shape of foils, were studied concerning the phase analysis, cell parameters, texture, and microstructure observations. The Bi_2−x Sb _x Te alloys were found to have the (2 0 $\bar 2$ 3) texture. The (2 0 $\bar 2$ 4) texture, with an additional (1 1 $\bar 2$ 0) component for x values greater than 0.4, was predominant for Bi_2−x Sb _x Te₂ foils. The electrical properties of these materials were then characterized by measuring the Seebeck coefficient, Hall coefficient, and electrical resistivity. It was found that Bi_2−x Sb _x Te foils changed from n- to p-type for an x-value of about 1.2. A maximum Seebeck coefficient, |α|, of 36×10⁻⁶ V K⁻¹ was measured for Bi₂Te. In the case of Bi_2−x Sb _x Te₂ foils, the change from n- to p-type was observed for an x value of about 1. A maximum Seebeck coefficient, |α|, of 32×10⁻⁶ V K⁻¹, was measured for Bi_1.4Sb_0.6Te₂. Measurements of the temperature-dependent electrical resistivity, Hall and Seebeck coefficients of the foils were carried out and the analysis revealed a semi-metallic behavior.