Thermodynamic stability, structural and electrical characterization of mixed ionic and electronic conductor La2Mo2O8.96

Abstract

Thermogravimetric analysis (TGA) technique in controlled oxygen partial pressure (pO₂) atmospheres has been used to obtain equilibrium oxygen content data as a function of pO₂ on the La₂Mo₂O_9−δ system resulting from the partial reduction of fast oxide-ion conductor La₂Mo₂O₉ (LM). Thermodynamic conditions for stabilization of crystalline La₇Mo₇O₃₀ and amorphous La₂Mo₂O_7−y at 718 °C have been determined and discussed. At 608 °C, the compound reported for the first time La₂Mo₂O_8.96 (LM896) has been found. The crystalline form and transition temperature in LM896 have been identified by X-ray diffraction at room temperature (XRD) and at controlled temperature. Conductivity curves obtained by electrochemical impedance spectroscopy (EIS) as a function of temperature for both LM and LM896 have been compared. The results indicate that LM896 is a mixed ionic and electronic conductor (MIEC).