Processing Effects on The Morphology of Hydrothermally Derived Nanocrystalline Lead Titanate
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PROCESSING EFFECTS ON THE MORPHOLOGY OF HYDROTHERMALLY DERIVED NANOCRYSTALLINE LEAD TITANATE. Zhiyuan Ye, Elliott B. Slamovich, and Alexander H. King School of Materials Engineering, Purdue University, West Lafayette, IN 47906, U.S.A. ABSTRACT Nanocrystalline lead titanate was synthesized by reacting nanocrystalline titanium oxide in aqueous solutions of potassium hydroxide and lead acetate at 200 degrees C. X-ray diffraction (XRD) and TEM studies suggest that the initial KOH concentration influenced the nucleation and growth behavior of the lead titanate nanoparticles. Powders were processed in aqueous solutions containing 0.10 M lead acetate and a Pb:Ti ratio of 1, with varying concentrations of KOH. Powders processed in 0.01 M KOH were composed of irregularly shaped particles with 50-100 nm in size, processing in 0.10 M KOH produced particles with finger-like morphology and broader particle size distribution, and processing in 1.0 M KOH resulted in anisometric plates with (001) facets, and 100-200 nm in size. XRD studies have shown systematic variations in the position and symmetry of reflections with a l component as a function of particle size. This indicates that the c/a ratio of lead titanate increases with decreasing nanoparticle size INTRODUCTION Hydrothermal processing, which involves reaction of aqueous solutions or suspensions of precursor and precipitation of complex oxides at elevated temperatures and pressures, has been widely applied in producing multicomponent metal oxide ceramic powders and thin films [1]. The ABO3 peroveskites, such as barium titanate and lead titanate, have been successfully fabricated by hydrothermal technique under various conditions [2-6]. Hydrothermal synthesis of high phase purity, ultrafine, crystalline PbTiO3 has been demonstrated by several groups at temperatures lower than 200 °C.[7-10] Compared to other processing methods such as solid-state reaction, sol-gel and coprecipitation, hydrothermal processing does not require going through a high temperature calcinations step, which causes particle coarsening and agglomeration [1]. Lower processing temperatures mean reduced energy budget. In the case of PbTiO3, elimination of calcinations step also avoids lead volatilization [11]. Furthermore, by varying the processing parameters like temperature, pH, and the reagent concentrations, it is possible to control the size distribution and the morphology of final products [1,9]. Hydrothermal synthesis of PbTiO3 has been extensively investigated experimentally and theoretically [3,4,7,10,11]. Thermodynamic calculations and experiments by Lencka and Riman [4] revealed the phase stability diagram under hydrothermal conditions. The phase stability diagram provided profound information about optimal process setup. However, the detail particle nucleation and coarsening mechanism remained unknown. Morphology studies not only were important for application, but also could provide more insight of the mechanism. Vast literatures have been devoted to the morphology [2,3,6,7,9]. High pH genera
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