Vaporization study of doped lanthanum gallates and Ga2O3(s) in H2/H2O atmospheres by the transpiration method

The vaporization of Ga2O3(s) and the doped lanthanum gallates La0.90Sr0.10Ga0.80Mg0.20O3−δ (LSGM-1020) and La0.80Sr0.20Ga0.80Mg0.20O3−δ (LSGM-2020) in H2/H2O atmospheres at temperatures between 973 K and 1173 K was investigated for the first time by the transpiration method. The equilibrium vaporization of Ga2O3(s) was elucidated as a function of temperature and the H2/H2O ratio. A vaporization reaction with GaOH(g) as most abundant vapor species is proposed. The enthalpy and entropy changes of this reaction were determined according to second and third law methods. In contrast to Ga2O3(s) the vaporization study of LSGM-1020 and LSGM-2020 was carried out under non-equilibrium conditions determining the transported mass of Ga, Mg, Sr and La by the H2/H2O carrier/reaction gas at constant temperatures for time periods of up to 600 h. The results obtained for Ga could be explained by a diffusion model which led to the determination of kinetic parameters for the diffusion and the vaporization.