ON THE POSSIBILITY OF PYROCHLORE PHASE-FORMATION IN ZINC-OXIDE VARISTOR CERAMIC

Formation of a pyrochlore phase and its transformation to the spinel phase in some multicomponent oxide mixtures has been investigated by X-ray diffraction. The effect of reaction temperature and material composition on the formation of pyrochlore phase and its lattice constant is discussed. In the system Bi2O3.Sb2O3.0.5 Cr2O3.0.5 MnO2.0.15 Co3O4.0.5 NiO, an almost pure pyrochlore phase with a= 1.0339(5) nm was formed at 950 degrees C. In the presence of ZnO the pyrochlore gradually transforms into spinel phase in the temperature range 690-1200 degrees C. The complete pyrochlore-->spinel transformation occurs below 1000 degrees C in the system 10 ZnO.Bi2O3.Sb2O3.0.5 Cr2O3.0.5 MnO2.0.15 Co3O4.0.5 NiO.