High-temperature ferroic phase transitions and paraelectric cubic phase in multiferroic Bi _0.95+δFe _0.9Zr _0.1O ₃

The temperature-dependent phase transitions of Bi _0.95+δFe _0.9Zr _0.1O ₃ have been studied using high-temperature x-ray powder diffraction together with differential scanning calorimetry measurements. The results show that Bi _0.95+δFe _0.9Zr _0.1O ₃ undergoes two phase transitions at 815 °C and 905 °C before decomposition at 920 °C. It appears that Zr-doping seems to stabilize the high temperature phases in such compound. Both the sharp contraction in the unit-cell volume and enthalpy thermal hysteresis demonstrate that the ferroelectric phase transition (α←→β) at 815 °C is of first order nature. In contrast, the highest β←→γ phase transition at 905 °C appears to be a second-order-like one. The analysis of the diffraction pattern in addition to Rietveld refinement strongly suggests a cubic symmetry for γ-phase.