Preparation Of Perovskite ABO₃ (A=Ba, Sr; B=Ti, Mn) Oxides By CHM Method

BaTiO₃,SrTiO₃ are typical perovskite-type (ABO₃) complex oxides. As new type of multi-functional materials, they are widely used in multilayer ceramic capacitors, grain boundary layer capacitors, piezoresistors and multi-functional sensors, etc. Currently, perovskite-type nanomaterials can be synthesized from solid, liquid and gas phase. For industrial production, solid phase synthesis has been commonly adopted. However, because the production process is often followed by milling and high-temperature annealing, powders prepared by this method consist of non-uniform, coarse particles and impurities, which can cause a low stability of the devices. Solution chemical method used to synthesize perovskite-type nanomaterials includes hydrothermal synthesis, sol-gel, coprecipitation and spray drying. Most of them involve high temperature annealing and/or high pressure, complex process, low crystallization and expensive raw materials, which are not suitable for industrialization.In this study, we developed a novel simple method-composite-hydroxide-mediated (CHM) route to synthesize well crystallized, highly pure, stoichiometrily precise BaTiO₃,SrTiO₃ and BaTi0.5Mn0.5O3 nanocrystals. This method only requires low synthesis temperature and pressure, which is beneficial for mass-production with low costs.As-synthesized BaTiO₃ by CHM are uniform, well dispersed nanoparticles, which have a cubic structure with sizes from 70 to100 nm. Experimental results indicated that higher temperature and longer growth time promoted the growth of particles with larger sizes. It was also found that a small amount of deionized water can induce the growth of the sphere shaped particles.The synthesized SrTiO₃ nanorods have lengths from 500 to 800 nm and widths about 100-150 nm, and exhibit plate-shape grains. The grains have lengths of 70 nm, width of ⁷0 nm and height of 5-10 nm. Between the grains, small dislocations were observed. Deionized water was also found to facilitate the growth of nanorods with the cubic structure.The BaTi0.5Mn0.5O3 elliptical nanorods synthesized by CHM method shows a hexagonal perovskite structure. Typical nanorods have widths ranging from 20 to 50nm, and lengths from 100 to 500 nm.The growth model of BaTiO₃ and SrTiO₃ was prospered by combining the growth unit model of anion coordination polyhedron and the aggregative growth model. We suggest that Ti(OH)610-unit is the favored growth unit, and the crystal growth follows the dissolution-crystallization-aggregative growth-recrystallization mechanism.Photoluminescence properties of the synthesis nanostructured were also investigated at the room temperature. It was found that when excited by the 350nm laser, pure BaTiO₃ powders show a weak emission peak at about 465nm. However, when 50% Ti is substituted by Mn, the as-synthesized BaTi0.5Mn0.5O3 exhibits bright emission peaks at about 465nm and 593nm, respectively.