Anomalous Expansion in the Firing Process of Piezoelectric Ceramics Containing PbO

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Abstract
Experimental studies were made on the firing process of the piezoelectric ceramics containg PbO such as PbZrO3, PbTiO3, Pb(Zr-Ti)O3, Pb(Ta0.5-Fe0.5)O3 and so on. The results obtained are summarized as follows. 1) When the powder mix of PbO⋅ZrO2 was heated at the constant rate of 300°C/hr in air, PbZrO3 was formed from the temperature about 600°C and the solid reaction was finished at the temperature of maximum expansion of about 1100°C. For specimens fired at the temperature above 1200°C, the pattern of ZrO2 was observed by X-ray diffraction and the ceramic density was decreased as compared with that fired at the lower temperature. This means that at this temperature PbZrO3 decomposes by the evaporation of PbO. 2) When the powder mix of PbO⋅TiO2 was heated, PbTiO3 was formed from the temperature about 500°C and the solid reaction was finished at about 800°C. 3) In the case of the raw mix of Pb(Zr-Ti)O3 ceramics, maximum expansion in the firing process was observed at 500°-600°C. The shrinkage curve fired in PbO atmosphere was considerably different from that fired in air. 4) In the firing process of the ferroelectric Pb(Ta0.5-Fe0.5)O3 ceramics from the raw mix of 4PbO+Ta2O5+Fe2O3, remarkably anomalous expansion was observed at 600°-900°C with the maximum linear expansion of 22%. This fact is very interesting in connection with the solid reaction.

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