Regularities of oxygen and water thermal desorption from barium cerate doped by neodymium, samarium, and gadolinium

Abstract

Processes of thermal desorption of oxygen molecules and water from BaCe_1–xM_xO_3–δ, where M= Nd, Sm, and Gd, presintered in air at the temperature of 650°C are studied. It is found that oxygen is desorbed only from neodymium–doped barium cerate and is almost not evolved from barium cerate doped by samarium and gadolinium. The amount of desorbed oxygen features a square dependence on cationic doping by neodymium. At similar degrees of cationic doping, the amount of water desorbed from neodymium–doped barium cerate is always lower than that from the cerate doped by samarium and gadolinium. The obtained experimental data on thermal desorption and analysis of literature data served as a basis for the conclusion as to the mixed valency of neodymium Nd(III)–Nd(IV) in BaCe_1–xNd_xO_3–δ. In this case, at similar doping degrees x, the hydration degree of BaCe_1–xNd_xO_3–δ is lower and the oxygen index is higher than in BaCe1_–x(Sm,Gd)_xO_3–δ. The differences become more pronounced at high degrees of cationic doping and must decrease at an increase in temperature.