Both mechanical and dielectric relaxation techniques were applied to investigate the microscopic transport mechanism of oxygen ion and to deduce the dynamical relaxation parameters in oxygen ion conductor ${\mathrm{La}}_2{\mathrm{Mo}}_2{\mathrm{O}}_9.$ In the mechanical relaxation measurement, a prominent relaxation peak was observed around 400 K at a measurement frequency of 1 Hz, which is actually composed of two subpeaks ${(P}_1$ at lower temperature and $P_2$ at higher temperature). As for the dielectric experiment, only one relaxation peak was observed above 600 K when the measurement frequency is greater than 500 Hz. The activation energy and the relaxation time at infinite temperature were determined as (0.9 eV, $3\times {10}^{-16}\hspace{0.5em}\mathrm{s}),$ (1.1 eV, $2\times {10}^{-16}\hspace{0.5em}\mathrm{s}),$ and (0.99 eV, $5\times {10}^{-14}\hspace{0.5em}\mathrm{s})$ for the $P_1$ peak, $P_2$ peak, and dielectric peak, respectively. These relaxation parameters are all in the same range as that for oxygen ion diffusion in oxide ceramics, suggesting a mechanism of short diffusion of oxygen ions for the two kinds of relaxation peaks. Based on the crystalline structure of ${\mathrm{La}}_2{\mathrm{Mo}}_2{\mathrm{O}}_9,$ an atomistic mechanism of oxygen ion diffusion via vacancies is suggested.

• Received 9 August 2001

DOI:https://doi.org/10.1103/PhysRevB.65.064304