Phase transitions in the BIZRVOX system

A combination of variable temperature X-ray powder diffraction, ac impedance spectroscopy and differential thermal analysis (DTA) has been used to characterise phase transitions in the Bi2ZrxV1−xO5.5−(x/2)−δ, BIMEVOX system. At low substitution levels α-, β-, and γ-phase BIMEVOX structures are observed as a function of temperature with some evidence for an intermediate phase, ɛ, seen between β and γ phases on heating. At x = 0.10 the β-phase is observed at room temperature with a transition to the γ-phase at around 500 °C. There is evidence for a subtle phase transition at around 200 to 250 °C in the variation of refined cell parameters and the Arrhenius plot of conductivity for this composition that may be associated with a vacancy ordering phenomenon. For the x = 0.19 composition, despite near equivalence of a and b unit cell parameters, variation in the unit cell c-parameter, DTA and Arrhenius plots of conductivity show evidence of a β↔γ transition between 450 and 500 °C and that the true symmetry of the low temperature phase is likely to be orthorhombic.