HIGH-TEMPERATURE X-RAY STRUCTURAL, THERMAL AND DIELECTRIC CHARACTERISTICS OF FERROELECTRIC BI2VO5.5

The X-ray powder diffraction, dielectric and thermal studies of bismut h vanadate (Bi2VO5.5) ceramic have been carried out as a function of t emperature (300-900 K). The high-temperature X-ray studies, supported by differential scanning calorimetry, clearly demonstrate that Bi2VO5. 5 undergoes two major phase transitions at similar to 730 and similar to 835 K. It was found that the one at 730 K is associated with both t he ferroelectric and the crystallographic transition, while at 835 K, Bi2VO5.5 undergoes only the crystallographic transition. Anomalies in both the dielectric constant and specific heat curves have been observ ed at similar to 730 and similar to 835 K. The total heat, Delta Q, an d entropy, Delta S, associated with the transition at 730 K were found to be higher than those at 835 K.