Phase equilibria and X-ray diffraction investigation of the system Cu−Fe−O

Abstract

An equilibria investigation for the system Cu−Fe−O determined nine regions of stability which were investigated in the oxygen pressure range of 1×10−4 to 5×10−1 atm (P total=1 atm) and at temperatures of 1173° to 1250°K. Oxygen dissociation pressures were determined for three univariant, four bivariant, and two trivariant equilibria. X-ray examination of selected equilibrated samples established conclusively that 1) cuprous ferrite (delafossite) is a stoichiometric compound, 2) cupric ferrite is a solid solution, and 3) solubility of delafossite in cuprous oxide is negligible. A relationship of lattice parameters with compositional variations was determined for the solid solution. Tetragonal-to-cubic spinel crystal transformation of cupric ferrite solid solution occurs with ac/a ratio at or slightly greater than 1.028. A volume discontinuity accompanies the tetragonal-to-cubic spinel transformation, which is a first-order type of thermodynamic transition.