Low-frequency internal friction study of oxide-ion conductor La2Mo2O9

The internal friction of oxide-ion conductor La2Mo2O9 has been measured using a computer-controlled torsion pendulum. Two internal friction peaks were observed around 380 K and 833 K respectively at a vibration frequency of 1 Hz and a heating rate of 5 K min(-1). The lower-temperature peak is of relaxation type and actually composed of two sub-peaks that originate from the disorder diffusion of two different kinds of oxygen ion in La2Mo2O9. The relaxation strength of the high-temperature component of this peak is much larger than that of the low-temperature component, which can be understood due to the different concentration of the two kinds of oxygen ion. As for the high-temperature peak at 833 K, it is associated with a first-order phase transition and corresponds to an order-disorder transition in aspects of oxygen ions. Substituting the La3+ cation to some degree with divalent Ca2+ can suppress this phase transition and maintain the high-temperature phase to lower temperature.