Vanadium Concentration Dependence of Thermoelectric Properties of β-Rhombohedral Boron Prepared by Spark Plasma Sintering

Abstract

Samples of 1 at% metal (Al, Co, Cr, Cu, Mo, Nb, Ni, Ru, Si, V, W, Zr)-doped β-rhombohedral boron (β-boron) were prepared by spark plasma sintering and their thermoelectric properties were examined in the temperature range from 353 K to 1073 K. It was found that V-doped β-boron exhibited the largest dimensionless figure of merit (ZT value). The V concentration dependence of the thermoelectric properties of β-boron was investigated. We discuss the effects of V doping into β-boron and the precipitation of a second phase on the thermoelectric properties. The temperature dependences of electrical conductivity and the Seebeck coefficient in the single-phase range of V concentration can be explained by assuming a combination of the band conduction of holes and the variable-range hopping conduction of electrons. This is described using the band structure model with the intrinsic acceptor level and the hybridization between the orbitals of boron and V, which corresponds to the metallic-covalent bonding conversion. Among the samples of V-doped β-boron, V2.0B105 had the highest value of ZT (7.91×10−3 at 1079 K) due to both V doping and the precipitation of a metallic phase (VB2).