Semiconducting properties and band structure of polycrystalline Bi4Mo20O62 compounds

Transport coefficient measurements (electrical conductivity, thermoelectric power and Hall effect) have been performed on compacted bars of Bi₄Mo₂₀O₆₂ in polycrystalline form over the temperature range (130–500 K) Experimental results are discussed in comparison to those obtained recently on Sb₄Mo₂₀O₆₂ They are interpreted on the basis of the same _p-type semiconductor model with two inverted deep levels near the midgap Conduction mechanisms are governed by acoustical-phonon scattering of the carrriers The top of the valence band is assumed to be formed from the d_xy orbitais of some of the Mo atoms leading to narrow bonding bands, while the donor and acceptor levels may be formed from the nonbonding d_xy orbitais of some of the Mo atoms of the distorted octahedron framework EPR measurements are discussed on the basis of this model and in comparison to the EPR results for Sb₄MO₂₀O₆₂ It is assumed that more than one narrow energy level (localized d states located below the valence band) contributes to the area of the line The XPS spectrum obtained on Bi₄Mo₂₀O₆₂ is also discussed.