Non-adiabatic polaron hopping conduction in semiconducting V₂O₅-Bi₂O₃ oxide glasses doped with BaTiO₃

Abstract

BaTiO₃-doped (5–40 wt %) 90V₂O₅-10Bi₂O₃ (VB) glasses have been prepared by a quick quenching technique. The d.c. electrical conductivities, σ_d.c., of these glasses have been reported in the temperature range 80–450 K. The electrical conductivity of these glasses, which arises due to the presence of V⁴⁺ and V⁵⁺ ions, has been analysed in the light of the small-polaron hopping conduction mechanism. The adiabatic hopping conduction valid for the undoped VB glasses (with 80–95 mol % V₂O₅), in the high-temperature region, is changed to a non-adiabatic hopping mechanism in the BaTiO₃-doped VB glasses. At lower temperatures, however, a variable range hopping (VRH) mechanism dominates the conduction mechanism in both the glass systems. Such a change-over from adiabatic to non-adiabatic conduction mechanism is a new feature in transition metal oxide glasses. Various parameters, such as density of states at the Fermi level N(E_F), electron wave-function decay constant, α, polaron radius, r _p, and its effective mass, m ^*_p , etc., have been obtained for all the glass samples from a critical analysis of the electrical conductivity data satisfying the theory of polaron hopping conduction.