Synthesis and properties of oxide ion conductor Pr₂Mo₂O₉ with La₂Mo₂O₉ structure

Abstract

Polycrystalline Pr₂Mo₂O₉ samples have been prepared by solid-state synthesis and single crystals of this compound have been grown. Pr₂Mo₂O₉ is unstable in the temperature range 700–900°C and partially decomposes with the formation of Pr₂Mo₃O₁₂ at these temperatures, but upon further heating to 1000–1050°C, Pr₂Mo₂O₉ is recovered. At room temperature, the structure, polymorphism, and physical properties of Pr₂Mo₂O₉ are similar to those of the known oxide ion conductor La₂Mo₂O₉. Pr₂Mo₂O₉ exhibits a reversible first-order phase transition to the cubic phase in the temperature range 520–540°C. The electric conductivity of Pr₂Mo₂O₉ is close to that of La₂Mo₂O₉ and amounts to 3.5 × 10⁻² S/cm at 700°C. The conductivity of Pr₂Mo₂O₉ is described by the Arrhenius law in the low-temperature phase and by the Vogel-Fulcher-Tammann equation in the high-temperature phase.