Thermoelectric properties of metal-doped β-rhombohedral boron

beta -Rhombohedral boron (beta -rh, boron) was doped with V, Cr, Fe, Co, or Zr to investigate the relationship between occupancies of the doping sites and thermoelectric properties. Doping with V or Cr, which preferentially occupy the A(1) sites, produces an increase in electrical conductivity and a negative Seebeck coefficient, while doping with Fe or Co, which occupy the A(1) and D sites equally, also increases the electrical conductivity though the Seebeck coefficient remains positive, Doping with Zr, which does not occupy the A(1) sites, slightly increases the electrical conductivity with a resultant larger Seebeck coefficient. Regarding Co- and Zr-doubly doped p-type beta -rh, boron, both properties are determined mainly by Co content. The observed temperature dependence of the electrical conductivity of metal-doped beta -boron clearly indicates variable range hopping conduction such that both properties increase with increasing temperature up to room temperature, in contrast to the behavior of ordinary metals and semiconductors. The power factors of Go-doped p-type beta -rh, boron and V- or Cr-doped n-type beta -rh, boron increased with increasing temperature, and doping with about 1 at.% metal atoms produced materials whose power factor at room temperature is three to four orders of magnitude larger than that of pure beta -rh. boron, Finally, 1 at.% Co doping decreased the thermal conductivity of beta -rh, boron from 16 to about 4-2 W/m.K, with the maximum ZT of p-type Co1.0B105 being subsequently estimated as 1.0 x 10(-6) at room temperature, (C) 2000 Academic Press.