Influence of carrier doping on thermo- and galvano-magnetic effects of Bi88Sb12 alloys

Abstract

In this study, the influence of carrier doping on the thermo- and galvano-magnetic effects of Bi–Sb alloys was investigated. Seven types of Bi88Sb12 alloys, namely, the undoped and 0.01, 0.02, and 0.04 at. % Te- and Sn-doped alloys, were fabricated via the spark plasma sintering method and solid phase reaction. The magnetic field dependencies of the diagonal resistivity, Hall resistivity, thermal conductivity, Seebeck thermopower, and Nernst thermopower were measured in the range of −5–5 T at 300 K, and the dimensionless figures of merit for the Seebeck and Nernst effects, i.e., the zST and zNT, respectively, were determined. As a result, both the zT values in the magnetic field were improved by the addition of a trace amount of Te. To better understand this behavior, a computational model that qualitatively describes the Seebeck, Nernst, magnetoresistance, and Hall effects, as well as the carrier thermal conductivity of Bi in the magnetic field, was developed based on the Boltzmann equation by considering the relaxation time approximation. The influence of carrier doping on the thermo-magnetic effect was considered by shifting the chemical potential with the rigid-band model in the established computational model. The computational results demonstrated that zST and zNT in the magnetic field were improved by shifting the chemical potential. These findings revealed that carrier doping could be a promising approach to improve the zT, namely, the zST for the Seebeck effect and zNT for the Nernst effect in Bi–Sb alloys in a magnetic field.