Microstructural and dielectric properties of KCl-added bismuth vanadate ceramics

Abstract

The effect of KCl addition on the microstructural, structural and dielectric properties of bismuth vanadate, Bi ₂ VO _5.5 (BiV) has been examined. The average grain size of BiV ceramics increases with increase in KCl content (from an average grain size of 10 to 80 µm) as a result of the increased liquid-phase formation of KCl, at the grain boundaries. Differential scanning calorimetry (DSC) carried out on the KCl-added samples indicates an upward shift in the transition temperature (T _c ), from 723 K (for BiV) to 734 K (for 5 mol% KCl-added BiV). On further increase in the KCl content, T _c shifts down to about 722 K for 10 mol%. This trend is consistent with that of the lattice strain data. The relative permittivity as well as the dielectric loss decrease by more than half of the original values upon the addition of KCl. The relative permittivities of the KCl-added ceramics are comparable with the values predicted by the logarithmic mixture rule. Impedance analyses suggest that the grain boundary resistance of the KCl-added BiV ceramics is higher by two orders of magnitude than that of BiV ceramics. The KCl-added BiV ceramics exhibit ferroelectric domains and the domain density decreases as the grain boundary region is approached.