Synthesis and characterization of compositionally modified PZT by wet chemical preparation from aqueous solution

doi:10.1016/S0955-2219(03)00428-X

Journal of the European Ceramic Society

Volume 24, Issue 6, 2004, Pages 925-929

https://doi.org/10.1016/S0955-2219(03)00428-X Get rights and content

Abstract

Compositionally modified PZT powders of Nb-doped PZT and PMN–PZT were synthesized via two processing routes, namely coprecipitation and evaporative decomposition. The new precursor of Zr_xTi_1−x-peroxo-nitrate solution was stable and suitable for the synthesis processes. For Nb-doped PZT, reactive fine powders of single-phase perovskite were formed at temperature as low as 600 °C in both methods and fairly high specific surface areas of 17 m²/g (coprecipitation) and 8 m²/g (evaporative decomposition) were obtained for the synthesized powders. For PMN–PZT, evaporative decomposition process effectively yielded the phase-pure perovskite without the pyrochlore at 700 °C.

Introduction

Wet chemical process has been extensively studied for the synthesis of various ceramic powders due to the merits of easy composition control, better homogeneity and low processing temperature in comparison to the conventional solid-state reaction process. Among the chemical processes, coprecipitation technique has been most widely investigated to prepare compositionally modified lead zirconate titanate (PZT) ceramics.1, 2, 3, 4 Coprecipitation uses low cost precursors of inorganic salts, such as metal chlorides or nitrates, and has considerable practical merits to prepare commercially viable powders. Although the process has achieved great successes in preparing the PZT ceramics, still some limitations, such as a preferential precipitate formation and an incomplete precipitation, may occur. For example, the preferential precipitate of lead (Pb) chloride, which is hard to re-dissolve, is easily formed in mixed chlorides and nitrates solutions prior to the coprecipitation.³ To avoid the lead chloride precipitation and chlorine contamination in the prepared powders, aqueous solutions of metal nitrates are often used as precursors to prepare some PZT powders.2, 3, 4 In the starting materials, however, titanium (Ti) nitrate solution is highly unstable to temperature and solution pH. Therefore, the solution must be stored in a refrigerator and kept at strong acidity.⁵ Furthermore, the coprecipitates, such as metal hydroxides or oxalates, have different solubilities in the reaction solution and washing media (distilled water or alcohols), which leads to the incomplete precipitation. Especially, for PMN–PZT {Pb(Mg_1/3Nb_2/3)O₃–PbZr_xTi_1−xO₃} powders, Mg²⁺ has high solubility for most precipitants, and hence causes an incomplete precipitation of the magnesium component.

In the present study, compositionally modified PZT ceramics of Nb-doped PZT and PMN–PZT at near the rhombohedral–tetragonal morphotropic phase boundary (MPB) were prepared by wet chemical processes. To synthesises the single-phase powders at low temperatures and to overcome the described problems, coprecipitation and evaporative decomposition with use of modified nitrates based solutions are adapted.

Section snippets

Experimental

Nb-doped PZT (PbZr_0.53Ti_0.47O₃₊0.5 wt.% Nb₂O₅) and PMN–PZT {0.375Pb(Mg_1/3Nb_2/3)O₃–0.625PbZr_0.4Ti_0.6O₃} powders of near the MPB compositions were prepared by the coprecipitation and the evaporative decomposition method.

Aqueous solutions of reagent grade Pb-nitrate, Mg-nitrate and Nb-ammonium oxalate were used as precursor materials. For both the Zr and Ti components, the new precursors of Zr_x·Ti_1−x-peroxo-nitrate (x=0.4 and x=0.53) complexes were used. The Zr_x·Ti_1−x-peroxo-nitrates for the

Stability of Zr_x·Ti_1−x-peroxo-nitrates solution

Aqueous solution of TiO(NO₃)₂, as a Ti source in PZT preparation, is known to be unstable under normal conditions, as mentioned.⁵ Hydrous TiO₂ is easily formed in the solution and the quantity of TiO₂ increased with increasing temperature. Therefore, all the reaction temperatures during preparation process must be kept less than 15 °C and the solution stored in a refrigerator. Furthermore, the solution becomes stable only when the pH was kept at less than 0.2. In this study, it was found that

Conclusion

Compositionally modified PZT powders were prepared by coprecipitation and evaporative decomposition process. In this study, the modified wet chemical approaches by using the Zr_x·Ti_1−x-peroxo-nitrate solutions were found to be quite applicable routes for the powder synthesis at lower temperatures.

For Nb-doped PZT, the processing temperatures of perovskite phase synthesis and dense ceramic formation were substantially lowered in both wet chemical methods. Coprecipitation was more effective to

Acknowledgments

This article was financially supported by the Research Center for Electronic Ceramics (RCEC) of Dongeui University funded by the Korea Science and Engineering Foundation (KOSEF), Ministry of Science and Technology (MOST) and the Busan Metropolitan City Government.

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Synthesis and characterization of compositionally modified PZT by wet chemical preparation from aqueous solution

Abstract

Introduction

Section snippets

Experimental

Stability of Zrx·Ti1−x-peroxo-nitrates solution

Conclusion

Acknowledgments

J. Euro. Ceram. Soc.

Mater. Lett.

Mater. Lett.

Mater. Lett.

Reactive PZT precursor powder by coprecipitation

Mater. Lett.

Stability of Zr_x·Ti_1−x-peroxo-nitrates solution