Crystallization kinetics of homogeneously precipitated lead zirconate titanate using urea: Comparison with the conventio
- PDF / 316,203 Bytes
- 8 Pages / 585 x 783 pts Page_size
- 40 Downloads / 142 Views
Ultrafine, PbZr0.53Ti0.47O3 powder was synthesized by homogeneous precipitation of metal ions in aqueous solution using urea. The results obtained from different characterization methods were compared with those obtained from the conventional precipitation method using ammonia in terms of crystallization, homogeneity, and microstructure. The as-dried precipitate converted to the single-phase crystalline lead zirconate titanate powder when calcined at 550 °C and above. The calcined powder showed smaller particle size, minimum agglomeration, and uniform shape. The growth of the particles was very little at higher temperatures. Powdered samples that precipitated using urea crystallized directly to rhombohedral lead zirconate titanate, without any intermediate pyrochlore phase formation. The NH3-precipitated powder converted to rhombohedral lead zirconate titanate 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.
I. INTRODUCTION
Lead zirconate titanate (PZT) is a ferroelectric ceramic widely used as a piezoelectric material in many sensor and actuator applications because of its large electromechanical coupling coefficient and high resistance to depolarization.1 PbZr0.53Ti0.47O3 where the Zr/Ti ratio is within the morphotropic phase boundary has the highest dielectric constant and is therefore a preferred capacitor material.2 In the morphotropic phase, boundary region ferroelectric rhombohedral and ferroelectric tetragonal phases coexist and the width of this two-phase region depends on the distribution of Zr and Ti at the atomic scale. The electromechanical properties are directly related to the crystal chemistry, homogeneity, and microstructure. The presence of an additional phase even in small amounts affects the electrical properties. Considerable work has been conducted on the chemical synthesis of PZT powders, which includes sol-gel,3–6 hydrothermal,7,8 coprecipitation,9 and gel combustion10 syntheses. Among these chemical techniques, sol-gel and coprecipitation synthesis account for maximum and least attention, respectively. Homogeneous precipitation of single and binary metal oxides using urea as a precipitation agent has been one of
the most focused soft chemical methods in the recent years.11–15 Many authors have reported low crystallization temperature, better homogeneity, and high reactivity in the homogeneously precipitated ceramic powders, which eventually offers lower processing temperatures. For PZT and PZT-based ceramics, better homogeneity in the precursor powder decreases the possibility of pyrochlore phase formation, which is detrimental for the final properties. A lower processing temperature is helpful in minimizing the Pb loss from evaporation of PbO at higher temperatures. Tas¸ et al.16 reported the synthesis of pure perovskite PZT powder from metal chlorides as the precursor material in a coprecipitation reaction and
Data Loading...
