Precipitation of Zirconia Phase in Niobium-Modified Ceramics of Lead Zirconate-Titanate

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Abstract
The piezoelectric performances of lead ziroconate-titanate ceramics are much improved by an addition of niobia, and they are called the “modified” ceramics by the staffs of the Clevite Research Center. Microscopic observation of these ceramics shows many pink precipitates segregating out of the grains. These parts are luminescent in the incidence of electron beam. The electron probe microanalysis reveals that they are rich in Zr and poor in Ti, Nb and Pb. The amount of these parts increases with the addition of niobia. In the x-ray diffraction measurement, the lines characteristic to the baddeleyite-type structure become observable with increasing amounts of niobia, though much weaker than perovskite type spectra. These facts lead us to the conclusion that a niobium ion occupies a Ti-Zr site by expelling out a ziroconium ion and as a result, the modified ceramics consist of two phases, the baddeleyite-type zirconia phase and the perovskite-type solid solution phase. The latter has a composition Pb1-x/2 ((Zr y -Ti1-y )1-x -Nb x )O3. The comparison of the physical properties of the solid solution ceramics with those of the modified ones gives a further evidence for this expectation.