Phase equilibria and properties of complex oxides in the ½ Eu2O3 – ½ Fe2O3 – CoO system

Abstract

Phase equilibria in the ½ Eu₂O₃ – ½ Fe₂O₃ – CoO system are studied at 1100 °C in air. A continuous series of EuFe_1-xCo_xO_3-δ solid solutions between europium ferrite and europium cobaltite with an orthorhombically distorted perovskite structure (SG Pbnm) has been confirmed. The unit cell parameters and unit cell volume of EuFe_1-xCo_xO_3-δ solid solutions obey Vegard's law. The homogeneity ranges of solid solutions in quasi-binary ½ Fe₂O₃ – CoO constituent subsystems at 1100 °C in air, taken from various works, are analyzed, and a phase diagram for the ½ Eu₂O₃ – ½ Fe₂O₃ – CoO system, consisting of 4 two-phase and 3 three-phase fields is constructed. The oxygen content in EuFe_1-xCo_xO_3-δ solid solutions is determined by the hydrogen reduction and iodometric titration methods. Oxygen losses with increasing temperature are small, maximum oxygen deficiency δ at 1000°C does not exceed 0.05. Linear thermal expansion of EuFe_1-xCo_xO_3-δ ceramics was measured by dilatometry. The nonlinear behavior of the dilatometric curves is discussed in terms of a possible change in the spin state of Co³⁺ ions. Electrical conductivity, which is low at room temperature and does not differ for all the samples studied, increases significantly with increasing temperature and Co content.