Thermogravimetric and desorbed-gas analyses of perovskite-type Ba(ZnxNb11x)Oy(OH)z

Abstract

Polycrystalline samples of perovskite-type Ba(ZnxNb11x)O31¤ with 0 ¯ ¤ ¯ 0.5 [¤ = (3x 1 1)/2; 1/3 ¯ x ¯ 2/3] were characterized by means of thermogravimetry (TG) combined with gas chromatography (GC). The TG-GC experiments on the Ba(ZnxNb11x)O31¤ samples revealed that these oxides are subject to water incorporation under humid atmospheres, and exhibit multiple steps of water desorption upon heating up to 873 K. The largely different desorption temperatures among these steps indicate a variety of water species being incorporated in different forms, such as physically/chemically adsorbed water molecules and hydroxide ions. For each sample, the number of hydroxide ions and thereby a nominal composition in an oxy-hydroxide form were quantitatively estimated. The total amount of the incorporated water species tends to increase as the oxygen deficiencies (¤) increase. The highly oxygen-deficient samples with ¤ = 0.4 and 0.5 were found to show significantly enhanced electrical conductivity at temperatures between 623 and 773 K in a humid atmosphere. The enhancement may be attributed to the additional contribution of proton conduction associated with the incorporated hydroxide ions.