Hydrothermal processing of lead titanate powders and thin films.

摘要

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.