Ionic and electronic conductivity in some alkali vanadates

The electrical conductivity (σ) and thermoelectric power (S) of pressed pellets of Li3VO4, Na3VO4 are presented in the temperature range from 440 K to the melting point of each solid. The ionic (σi) and electronic (σe) contributions to σ have been separated over the entire temperature range with the help of time dependence study of the dc electrical conductivity. Super-ionic phases in all three solids have been observed well below their melting point in which the conductivity is almost purely ionic. The value of the phase transition temperature below, which the solid transforms from super-ionic to normal phase, has been obtained. It has been shown that in the normal phase, these solids are mixed conductors. Data for the temperature variations of both σi and σe are also presented and discussed.