GRAIN-SIZE EFFECTS ON THE DIELECTRIC-PROPERTIES OF FERROELECTRIC BI2VO5.5 CERAMICS

Dielectric properties and microstructural characteristics of ferroelectric bismuth vanadate (Bi2VO5.5) ceramics exhibiting grain sizes of 7, 10, 20 and 25 mum have been studied. Microstructural studies indicate the presence of ferroelectric 90-degrees domain patterns on the surface as well as in the bulk of the coarse-grained ceramics. The dielectric constant and the loss tangent both at room temperature and in the vicinity of the Curie temperature have been found to increase with increasing grain size. The Curie temperature (725 K) is found to shift slightly (by about 7 K) towards higher temperatures as the grain size increases (7-25 mum). The magnitude of the dielectric anomaly around 725 K is found to be higher for coarse-grained ceramics. The dielectric constant and the loss have been found to decrease with increase in frequency (1-100 kHz) for all the ceramics studied. The increase in dielectric constant with increasing grain size is attributed to a decrease in thickness of the relatively more insulating grain boundary layer.