THE ROLE OF MICROSTRUCTURE AND PROCESSING ON THE PROTON CONDUCTING PROPERTIES OF GADOLINIUM-DOPED BARIUM CERATE

The influence of grain boundary conductivity and microstructure on the electrical properties of BaCe0.85Gd0.15O3-delta have been examined. G rain sizes were varied by sintering at various temperatures. Impedance data were analyzed using the brick layer model, and some new conseque nces of this model are presented, The specific grain boundary conducti vity exhibits an activation energy of similar to 0.7 eV, and for simil ar processing routes, is Independent of grain size. An isotope effect was observed, indicating that protons (or deuterons) are the mobile sp ecies. TEM investigations showed the intergranular regions to be free of any glassy phase that could account for the differences in bulk and grain boundary propel-ties. Single-crystal fibers, grown by a modifie d float zone process, were notably barium deficient, and exhibited a l ow conductivity,comparable to that of polycrystalline Ba0.96Ce0.85Gd0. 15O3-delta.