Phase Diagram Calculations of ZrO_2-Based Ceramics with an Emphasis on the Reduction/Oxidation Equilibria of Cerium Ions in the ZrO_2-YO_(1.5)-CeO_2-CeO_(1.5) System

摘要

Phase diagram calculations that were made previously for the ZrO_2-MO_(m/2)(m = 2, 3, 4) systems and for the ZrO_2-YO_(1.5)-MO_(m/2) (M = transition metals) systems have been extended to the ZrO_2-YO_(1.5)-CeO_2(-CeO_(1.5)) system to make an attempt to explain (1) thermogravimetric (TG) results as a function of oxygen potential, (2) electronic conductivity as a function of oxygen potential, and (3) a miscibility gap observed in air. The interaction parameters for the CeO_2-CeO_(1.5)-YO_(1.5) system were obtained from the reported oxygen nonstoichiometry in CeO_(2-x) and rare earth doped ceria, (Ce,RE)O_(2-#delta#) The interaction parameters for the ZrO_2-CeO_2 subsystem were obtained so as to reproduce the observed miscibility gap at 1273 K. Those thermodynamic properties can reproduce consistently the experimental behaviors of the electronic conductivity and the TG results in the (Zr_(1-x)Ce_x)_(0.8)Y_(0.2)O_(1.9) solid solutions; these indicate the enhancement of reduction of CeO_2.