STABILITY OF CUBIC ZRO2 (10 MOL-PERCENT Y2O3) WHEN ALLOYED WITH NIO, AL2O3 OR TIO2 - IMPLICATIONS TO SOLID ELECTROLYTES AND CERMETS

This work uses room temperature X-ray diffraction and electron microscopy to investigate the solution of NiO, Al2O3 or TiO2, in cubic (c-) ZrO2, (with 10 mol.% Y2O3, designated as yttria fully stabilized zirconia (Y-FSZ)) powders and the consequent destabilization, if any, of Y-FSZ. After sintering at 1600 degrees C for 4 h, the dissolution of the additives (the solubilities are > 15 mol.% for TiO2, ca. 5-10 mol.% for NiO and rather limited for Al2O3) caused a smaller cell volume of c-ZrO2. Among the additives, only TiO2 causes the precipitation of tetragonal (t-) ZrO, in c-ZrO, matrix. The increased solution of TiO2 in Y-FSZ results in a larger tetragonality of t-ZrO2, but the t-ZrO2 precipitates remain as twin-related colony structure with {101} habit plane, the same as for the ZrO2-Y2O3 system. Due to oversaturation, the added NiO or Al2O3 appears as second phase particles which hindered the grain growth of c-ZrO2. The implication of these results to zirconia electrolyte cell and metal/ceramic joints such as thermal barrier coating (TBC) are discussed.