Band structure of polycrystallineSb4Mo20O62compounds

Abstract

Transport-coefficient measurements (electrical conductivity, thermoelectric power, and Hall coefficients have been performed on a compact ${\mathrm{Sb}}_{4}$${\mathrm{Mo}}_{20}$${\mathrm{O}}_{62}$ polycrystalline compound in a wide temperature range (130-500 K). Experimental results are interpreted with the help of a $p$-type semiconductor model with two inverted deep levels near the mid-gap. Conduction mechanisms are governed by acoustical-phonon scattering of the carriers. EPR measurements confirm the theoretical model, which has been retained. Lastly, the model is discussed on the basis of an idealized projection of the ${\mathrm{Sb}}_{4}$${\mathrm{Mo}}_{20}$${\mathrm{O}}_{62}$ structure. The top of the valence band is assumed to be formed from the ${d}_{\mathrm{xy}}$ orbitals of some Mo atoms leading to narrow bonding $\ensuremath{\pi}$ bands while the donor and acceptor levels may be formed from the nonbonding ${d}_{\mathrm{xy}}$ orbitals of some Mo atoms of the distorted octahedron framework.