Sintering Studies on 20 mol% Yttrium-Doped Barium Cerate

Acceptor-doped barium cerate perovskite oxides act as high temperature proton conducting ceramics, which can be utilized in solid oxide fuel cells, hydrogen separation membranes, and other electrochemical devices. One of the major issues in their fabrication is the formation of second phases during sintering of these perovskite oxides. In this work, the formation of a second phase is investigated with an aim to understand its influence on the properties of the parent perovskite oxide and also the necessity for its removal. BaCe(0.8)Y(0.2)O(3-delta) (BCY20) was synthesized via a polymeric sol-gel method and characterized by X-ray diffraction, scanning electron microscopy, and micro-Raman spectroscopy. Formation of the second phase on the surface of the sintered pellets (sintering temperature > 1250 degrees C for 24 h) was identified to be yttria-doped ceria (Y(0.2)Ce(0.8)O(1.9)). A mechanism for the formation of the second phase is proposed. The formation of second phase was prevented by sintering the pellets in a powder bath of the same composition as the parent perovskite oxide. From impedance spectroscopy measurements of pellets sintered with and without the powder bath, it was found that the second phase (in the pellet sintered without powder bath) has a negative effect on the bulk ionic conductivity of the pellet.