On the thermodynamic stability of La 2Mo 2O 9− δ oxide-ion conductor

Abstract

The stability of La 2Mo 2O 9− δ oxide-ion conductor was studied under Ar–H 2 and controlled oxygen partial pressure ( pO 2) 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). At 608 °C under Ar–H 2 flowing atmosphere, La 2Mo 2O 9 phase was found to be unstable and reduction leads to an amorphous phase with composition close to La 2Mo 2O 6.88. The stability of this amorphous phase under Ar–H 2 was analyzed by TCXRD and found to be stable below 900 °C. Isothermal TG under controlled pO 2 at 1000 °C indicated that La 2Mo 2O 9− δ is not stable below 10 −7 Pa and decomposition took place without the formation of La 7Mo 7O 30 or amorphization.