Phase transitions, electrical conductivity and chemical stability of BiFeO3 at high temperatures

The multiferroic perovskite BiFeO3 is reported to display two first order structural phase transitions. The structural phase transition at 925±5 °C is demonstrated to be first order by calorimetry and dilatometry. Electrical conductivity measurements revealed that the high temperature phase above 925±5 °C is semiconducting, in disagreement with recent reports. The sign and magnitude of the volumes of transition reflect the sign and magnitude of the discontinuities in electrical conductivity across the two first order phase transitions. A high partial pressure of oxygen was demonstrated to stabilise BiFeO3 towards peritectic decomposition. Finally, the origins of the commonly observed decomposition of BiFeO3 at high temperatures are discussed.