Effect of pH on the Crystallization of Homogeneously Precipitated Nanosized PZT Powder

Abstract

Nanosized lead zirconate titanate (PZT) powder with Zr:Ti ratio in the morphotropic phase boundary region was synthesized by homogeneous precipitation of metal ions. The powder precipitated at 90°C and at pH 6.7 resulted single-phase perovskite lead zirconate titanate powder when calcined at 550°C and above for 4 hours in air. The solution pH and the precipitation temperature strongly affect the composition of the calcined powder. The results obtained by structural characterization of homogeneously precipitated powder were compared with that obtained from the conventional precipitation method using ammonia in terms of crystallization, homogeneity, and microstructure. The homogeneously precipitated powder showed smaller particle size, minimum agglomeration and uniform shape on calcination and annealing. Powdered samples that precipitated by homogeneous precipitation crystallized directly to perovskite PZT, without any intermediate pyrochlore phase formation. In contrast, the NH₃ precipitated powder converted to perovskite PZT via metastable pyrochlore and it showed phase segregation upon annealing at higher temperatures. The reaction kinetics has been studied by X-ray diffraction, differential thermal analysis, and differential scanning calorimetry.

Keywords:

• Activation energy for crystallization
• Agglomeration
• Crystallization kinetics
• Enthalpy of crystallization
• Ferroelectric
• Homogeneous precipitation
• Morphology
• Morphotropic phase boundary
• Nanocrystalline
• Perovskite PZT
• Phase segregation
• Pyrochlore
• Rhombohedral
• Stoichiometric
• Tetragonal

ACKNOWLEDGMENTS

The authors thankfully acknowledge the financial support from the Defense Research Development Organization, Ministry of Defense, New Delhi, for carrying out the present work. The authors thank Director, D.O.A.C., ASL for providing facilities for thermal analyses.