High-temperature semiconducting cubic phase of BiFe0.7Mn0.3O3+δ

BiFe0.7Mn0.3O3+delta with space group R3c is reported to go through two phase transformations, first to the orthorhombic paraelectric phase (Pbnm) and finally to cubic perovskite structure with space group Pm (3) over barm. A discontinuity in volume and enthalpy shown by thermal analysis revealed that both transitions were first order. Electrical conductivity measurements demonstrated that the material remains semiconducting also in the high-temperature cubic state. The conductivity and the temperature of the two phase transitions were shown to be strongly influenced by the partial pressure of oxygen and a p-type semiconductivity was suggested. Finally, oxygen hyperstoichiometry (delta) of BiFe0.7Mn0.3O3+delta was demonstrated.