Synthesis of Sr‐ and Ba titanate particles coated on Al₂O₃substrates forming a core‐shell structure

Abstract

Sr‐ and Ba titanate particles doped with Nb, Mn, and Ce were produced via a wet‐chemical precipitation process based on salt solutions and metal chlorides around Al2O3 flake‐like particles. In a calcination process at high temperatures, a shell of doped oxides is formed that is responsible for the unusual electrical properties. The particles were investigated via scanning electron microscope (SEM) and transmission electron microscope which showed homogeneously covered Al2O3 particles. X‐ray diffraction exposed secondary phases besides BaTiO3 and SrTiO3 because of the high solubility of Ba(OH)2 and Sr(OH)2 in water and a resulting shortfall of earth alkaline metal. The oxidation states of the doping elements were determined via X‐ray photoelectron spectroscopy. Composite materials prepared from this filler and silicone rubber showed typical nonlinear voltage‐current (U‐I) characteristics, which are of special interest for high voltage engineering. The filler was evenly distributed within the matrix without settling while cross‐linking of the polymer, which was shown in an SEM‐backscattered electron image. The nonlinearity coefficient α, which is an important factor for field grading applications, was determined for different materials and reached a value of up to 7.