Electrical and optical properties of single crystals in the FeO–MnO systems

Abstract

The electrical conductivity of Fe_yMn_1−yO_1+x single crystals in equilibrium with various partial pressures of oxygen was measured in the temperature range 900–1150°C. When the conductivity data were plotted as functions of x or y, sigmoidally shaped curves were obtained. This composition dependence is consistent with a region of solid‐solid immiscibility within the (Fe,Mn)O phase field. The visible and near‐infrared absorption spectra of (Fe,Mn)O crystals exhibited crystal‐field peaks characteristic of both the Mn²⁺ and Fe²⁺ cations. The position of Fe²⁺ peaks was found to shift with MnO content although the peaks corresponding to the Mn²⁺ ion did not shift. It was concluded that the manganese ions are located on undistorted lattice sites which may be grouped into phase‐separated regions. Thus, both the electrical and optical results reflect a miscibility gap in the pseudobinary phase field.