Analysis of oxidation decomposition reaction scheme and its kinetics of delafossite-type oxide CuLaO2 by thermogravimetry and high-temperature X-ray diffraction

摘要

The oxidation decomposition reaction and its reaction kinetics of delafossite-type oxide CuLaO2, which is a mother phase of new luminescent material, at various temperatures were investigated by thermogravimetry and high-temperature X-ray diffraction. It was clarified that CuLaO2 is not thermodynamically stable in air and reacts with O-2, which is represented as the chemical reaction formula, 4CuLaO(2) + O-2 -> 2CuLa(2)O(4) + 2CuO, above 500 A degrees C. It was also revealed that CuLaO2 transforms to a metastable CuLaO2.66 phase with a copper valence of 2.32+ and some phases with lower crystallinity below 500 A degrees C. At 800 A degrees C, a metastable defect perovskite Cu2La2O5 phase was generated at initial period of the decomposition, resulting in variation to mixture of CuLa2O4 and CuO as reaction proceeded. It was found that a first-order reaction model can be applied to the reaction kinetics of the oxidation decomposition reaction. The activation energy for the reaction was estimated to be 65 kJ mol(-1) under air flow. It was concluded that CuLaO2 has lower kinetic stability than the other delafossite-type oxides such as CuAlO2 and CuGaO2.