Hydrothermal processing of lead titanate powders and thin films
Abstract
The influence of processing parameters on the formation and morphology of hydrothermally derived lead titanate (PbTiO3) powders was investigated. These experimental findings were then used to establish hydrothermal synthesis conditions under which continuous sub-micron PbTiO3 thin films could be processed. PbTiO3 powder was synthesized by suspending nanocrystalline powders of TiO2 in aqueous solutions of KOH and Pb(CH3COO) 2.3H2O at temperatures ranging from 120 to 200°C. PbTiO3 growth initiated in the ⟨100⟩ exposing (001) surfaces, and resulted in a faceted platelet morphology. Particle growth proceeded by further nucleation and growth on existing (001) surfaces. Through repeated dissolution and precipitation, the platelet clusters coarsened into larger cuboidal particles. PbTiO3 particle size was controlled by either inhibiting or promoting dissolution-precipitation. Dissolution-precipitation was inhibited by lowering the KOH concentration, reaction temperature, or maintaining an excess of Pb relative to Ti ions in solution, while it was promoted by increasing the KOH concentration and temperature. Coarsening of PbTiO3 particles coincided with decreases in: the x-ray diffraction (XRD) peak breadth, the asymmetry of l component XRD reflections, and the c-axis length. PbTiO3 and PbTiO3/polymer thin films were synthesized from a metallo-organic precursor on metallized quartz substrates. Titanium dimethoxy dineodecanoate (TDD) was spin-cast onto the substrates and converted to polycrystalline TiO2 via hydrolysis in deionized water for 5 h at 80°C. Polycrystalline PbTiO3 films were then formed by reacting the TiO2 films for 4 h at 200°C in aqueous solutions of KOH and Pb(CH3COO)2.3H 2O. Low KOH concentrations suppressed film coarsening, thereby facilitating the formation of fine-grain continuous PbTiO3 films. PbTiO 3/polymer thin films were processed in the same manner after first dissolving TDD and a polystyrene/polybutadiene triblock copolymer in p-xylene. PbTiO 3 and PbTiO3/polymer films had relative permittivities of ≈56 and 34 and dielectric strengths of ≈250 and 850 kV/cm, respectively.
Degree
Ph.D.
Advisors
Slamovich, Purdue University.
Subject Area
Materials science
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