Crystallization of lanthanum-modified lead zirconate titanate (Plzt) using coprecipitated gels

Powders of lanthanum-modified lead zirconate titanate (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)_0.98O₃ (PLZT 9/65/35) were obtained by calcination of various precursors via chemical coprecipitation methods. The precursors included the coprecipitated gel with the stoichiometric PLZT composition, PbO (powdered chemical reagent)+LZT coprecipitated gel, and mixture of Pb, La, Zr, and Ti individually precipitated gels. Crystallization behaviors of these precursors were examined over the temperature range of 400°-900°C using X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis/thermal gravimetric analysis (DTA/TGA) techniques. For coprecipitated PLZT gels, perovskite PLZT accompanied by pyrochlore crystallized at 500°C; further heating promoted the development of PLZT, and single-phase PLZT was achieved at 700°C. For PbO + LZT coprecipitated gels, PLZT began to form at 550°C. The formation reaction was complete at 800°C and only a limited amount of pyrochlore intermediate was detected by XRD. For the mixture of Pb, La, Zr, and Ti gels, PLZT crystallized at 900°C, litharge, massicot, PbTiO₃(PT), and PbZrO₃(PZ) were formed as the intermediate phase instead of pyrochlore.