MICROSTRUCTURAL AND DIELECTRIC-PROPERTIES OF KCL-ADDED BISMUTH VANADATE CERAMICS

The effect of KCI addition on the microstructural, structural and diel ectric properties of bismuth vanadate, Bi2VO5.5 (BiV) has been examine d. The average grain size of BN ceramics increases with increase in KC l content (from an average grain size of TO to 80 mu m) as a result of the increased liquid-phase formation of KCI, 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 BN) to 734 K (for 5 mol% KCl-added BiV). On further i ncrease in the KCI content, T-c shifts down to about 722 K for 10 mol% . This trend is consistent with that of the lattice strain data. The r elative permittivity as well as the dielectric loss decrease by more t han half of the original values upon the addition of KCI. The relative permittivities of the KCl-added ceramics are comparable with the valu es predicted by the logarithmic mixture rule. Impedance analyses sugge st that the grain boundary resistance of the KCl-added BiV ceramics is higher by two orders of magnitude than that of BN ceramics. The KCl-a dded BN ceramics exhibit ferroelectric domains and the domain density decreases as the grain boundary region is approached.