Sinterability, reducibility, and electrical conductivity of fast oxide-ion conductors La_1.8R_0.2MoWO₉ (R=Pr, Nd, Gd and Y)

Abstract To examine the effect of La-site substitution on the performance of the fast oxide-ion conductor β-La₂MoWO₉, doped La_1.8R_0.2MoWO₉ (R=Pr, Nd, Gd and Y) electrolytes are synthesized via solid-state reaction. The structures and properties of the electrolytes are studied by X-ray diffraction, dilatometric analysis, scanning electron microscopy, and impedance spectroscopy. Pr, Nd, and Y substitutions decrease the sintering temperature and increase the average grain size. The as-sintered specimens are annealed at 873 K in humidified 25% H₂-N₂ to test their structural stabilities. Compared with Nd-doped and Gd-doped samples, Pr-doped and Y-doped specimens do not exhibit obvious surface degradation after reduction. Although all substitutions relatively enhance the low-temperature (<500°C) conductivity of La₂MoWO₉, only Pr substitution obviously increases the high-temperature conductivity of the corresponding electrolyte. The temperature dependence of La_1.8R_0.2MoWO₉ conductivity were well fitted to an Arrhenius model below 500°C and a Vogel-Tamman-Fulcher model above 500°C.