Phase formation during liquid phase sintering of ZnO ceramics

ZnO doped with Bi2O3 and Sb2O3 (ZBS), is the basic system for ceramic varistors. Phase formation during sintering of ZBS was measured in situ, using 1 mm thick samples and synchrotron X-rays. Sintering shrinkage was measured in different atmospheres by an optical method. Thermodynamic calculations were performed to explain phase formation, composition, stability of additive oxides and influence of the oxygen fugacity on sintering. Sb2O4, pyrochlore, trirutile and spinel were formed at temperatures of 500-800 degrees C. The oxidation of antimony was controlled by the oxygen partial pressure and affected both, phase formation and sintering kinetics, in the ZBS system.