On the thermodynamic stability of La2Mo2O9−δ oxide-ion conductor

The stability of La2Mo2O9−δ oxide-ion conductor was studied under Ar–H2 and controlled oxygen partial pressure (pO2) atmospheres within the range 608 ≤ T ≤ 1000 °C, by thermogravimetry (TG), X-ray Diffraction (XRD), Temperature Controlled X-ray Diffraction (TCXRD) and Scanning Electron Microscopy (SEM).  °C under Ar–H2 flowing atmosphere, La2Mo2O9 phase was found to be unstable and reduction leads to an amorphous phase with composition close to La2Mo2O6.88. The stability of this amorphous phase under Ar–H2 was analyzed by TCXRD and found to be stable below 900 °C. Isothermal TG under controlled pO2 at 1000 °C indicated that La2Mo2O9−δ is not stable below 10−7 Pa and decomposition took place without the formation of La7Mo7O30 or amorphization.