Impedance,dielectric and modulus analyses of compounds LiMnVO 4 and LiCuVO 4

Abstract

A comparative study is carried out between the non-humidity sensitive Li vanadates, LiMnVO₄ and LiCuVO₄, from 25 to 500°C at frequencies from 42 Hz to 1 MHz. The mobile ion hopping rate of LiMnVO₄ is found to be higher than that of LiCuVO₄ due to the lower LiMnVO₄ bulk and grain boundary activation energy values. Dielectric constant values from 25 to 500°C at frequencies from 42 Hz to 1 MHz revealed the presence of all types of polarisation. At the plots of LiCuVO₄ tan δ (dielectric loss) versus frequency, tan δ displays a peak at a frequency that shifts to higher values with temperature. At 400°C, the maximum losses appear at 1 kHz and at 500°C at 10 kHz. The modulus master curves of LiCuVO₄ and LiMnVO₄ suggested the presence of conduction processes with the same activation energy at different frequencies.