Screening of the possible boron-based n-type thermoelectric conversion materials on the basis of the calculated densities of states of metal borides and doped β-boron

In order to screen candidates for n-type boride-based thermoelectric materials, the energetics of solid solutions of metallic atoms (Zr, Cr, and V) in β-rhombohedral boron (β-boron) and the densities of states of metal-borides of the CrB-, FeB-, MoB-, AlB2-, ReB2-, CaB6-, and UB12- types of structures and some tetraborides (YB4, CrB4, WB4, and MgB4) have been calculated using a first-principle pseudopotential method within the local (spin) density approximation. It was properly concluded that Zr occupies the E site of β-boron while V and Cr occupy the A1 site. As for metal-monoborides and diborides, the ‘rigid band approach’ seems to be valid. The large negative Seebeck coefficient of FexCo1−xB is hopeful if Mottʹs explanation for the trend of the Seebeck coefficient for transition metal elements is valid for these borides. Y- or La- doped Ca(Sr, and Ba)B6 can also be expected to be useful.