THERMAL-BEHAVIOR OF BI4V2O11 - X-RAY-DIFFRACTION AND IMPEDANCE SPECTROSCOPY STUDIES

Bi4V2O11 powdered samples and single crystals were studied by high temperature X-ray diffraction and impedance spectroscopy to characterize the phase transitions. From high temperature X-ray diffraction on powders and single crystals, the alpha reversible arrow beta and beta reversible arrow gamma reversible phase transitions were observed. The beta reversible arrow gamma one is ferroelastic reversible arrow paraelastic but surprisingly the alpha reversible arrow beta transition also exhibits a ferroelastic character, with a 90 degrees switching of the a and b axis on cooling and/or, more scarcely, on heating. Impedance spectroscopy measurements were carried out using platelet shaped single crystals with well developed (001) faces. The corresponding sigma(parallel to) (001 plane) and sigma(perpendicular to) (c direction) bulk conductivities were obtained and compared with values from ceramic pellets. sigma(parallel to) values are close to those characterizing the pellets, and the anisotropy of the conductivity is evidenced by sigma(parallel to) values about 2 orders of magnitude larger than sigma(perpendicular to) ones. Slope changes observed in Arrhenius plots are in agreement with the phase transitions.