High-temperature semiconducting cubic phase ofBiFe0.7Mn0.3O3+δ

Abstract

${\text{BiFe}}_{0.7}{\text{Mn}}_{0.3}{\text{O}}_{3+\ensuremath{\delta}}$ 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 $Pm\overline{3}m$. 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 $(\ensuremath{\delta})$ of ${\text{BiFe}}_{0.7}{\text{Mn}}_{0.3}{\text{O}}_{3+\ensuremath{\delta}}$ was demonstrated.