Nature of electronic conductivity in olivine-like glasses and nanomaterials of Li2O-FeO-V2O5-P2O5 system

In previous research, we have investigated glasses and highly-conducting nanomaterials of Li2O-FeO-V2O5-P2O5 system. However, it was unclear which hopping centers (iron or vanadium ions) dominated in charge carrier transport. Therefore, this phenomenon was investigated by combination of Mössbauer spectroscopy and thermoelectric power measurements. The Seebeck coefficient in glasses was close to zero, but negative. After nanocrystallization, |S| increased significantly and remained negative in all the samples. Thermal treatment of the samples at elevated temperature (up to ca. 500 °C) in air resulted only in insignificant oxidation of iron ions. Considering both Mössbauer and thermoelectric power measurements, one can conclude that Fe2 +/Fe3 + ratio does not have major influence on electronic conductivity of studied samples. It is rather V4 +/V5 + hopping centers situated on highly disordered nanocrystallites shells that play major role in high electronic conductivity of nanocrystallized samples (up to 7 ⋅ 10−3 S/cm).