Structural and electrical properties of La 2− xBa xMo 2O 9− x/2 ( x = 0–0.18)

Abstract

La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18–0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La 2Mo 2O 9 is defined in range of 0.18 < x < 0.2. As the replacement degree of La 3+ by Ba 2+ increases, the bulk conductivity of La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) decreases initially and then increases, a minimum value at La 1.9Ba 0.1Mo 2O 8.95 exists. Hebb–Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La 2− x Ba x Mo 2O 9− x/2 ( x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La 1.84Ba 0.16Mo 2O 8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10 −6 K −1 between 298 and 1173 K.