Damping mechanism in the novel La₂Mo₂O₉-based oxide-ion conductors

In this paper, the microscopic diffusion mechanism of oxygen vacancies in the oxygen-ion conductors La_2-xA_xMo₂O₉ with A = Bi, K and x = 0-0.15 are studied by the low frequency internal friction measurements. An internal friction peak associated with the phase transition around 833 K and two relaxation peaks associated with the short-distance diffusion of oxygen vacancies were observed in all samples. With increasing K and Bi doping contents, the activation energies of both relaxation peaks increase; the high-temperature peak decreases in height while the other relaxation peak increases. The phase transition can be completely suppressed by 10% K or 15% Bi doping. It is found that the effect of K-doping is stronger than that of Bi-doping. Combining with the analysis of the crystal structure of La₂Mo₂O₉, the microscopic mechanism of oxygen vacancy diffusion for the two relaxation peaks are suggested.