Anelastic and dielectric studies of La2Mo2O9-based oxide-ion conductors

This paper reports the results of internal friction and dielectric relaxation studies on novel oxide-ion conductors (La1−xAx)2Mo2O9−δ (A = Ca, Bi, K; x = 0–0.075). Two relaxation peaks associated with short-distance diffusion of oxygen vacancies were observed. Doping at La site with different elements shifts both relaxation peaks towards higher temperature and increases the activation energy of oxygen ion diffusion. In the case of internal friction, the height of the higher temperature peak (dominant component) decreases with increasing dopant content, while the lower temperature peak increases slightly. In the case of dielectric relaxation, on the other hand, the variation of the peak heights as a function of doping content exhibits a maximum around 2.5% K and 4% Bi. Furthermore, in undoped and slightly doped La2Mo2O9 samples, there is an internal friction peak around 570 °C associated with the order–disorder phase transition. In heavily doped samples, this peak disappears, indicating that this phase transition is suppressed and the high temperature phase is stabilized.