Formation Mechanism of (001) Oriented Perovskite SrTiO_3 Microplatelets Synthesized by Topochemical Microcrystal Conversion

摘要

To develop a better understanding of the mechanism responsible for topochemical microcrystal conversion (TMC) from Aurivillius SrBi_4Ti_4O_(15) precursors to perovskite SrTiO_3 microplatelets, compositional/structural evolutions, morphological development, and reaction interface evolution of the (001) oriented SrBi_4Ti_4O_(15) microplatelets were investigated during the conversion process. The results show that multiple topotactic nucleation events of SrTiO_3 occurred directly on the surfaces of SrBi_4Ti_4O_(15) above 700 °C, while reacting zones of intermediate phase(s) with less Bi~(3+) contents were observed to form in the interior of SrBi_4Ti_4O_(15). Extensive exfoliation of the precursors occurred generally parallel to the (001) surfaces above 775 °C. At 950 °C, the original singlecrystal SrBi_4Ti_4O_(15) platelet was replaced by a polycrystalline aggregate consisting of (001) aligned SrTiO_3 crystallites and poorly crystallized intermediate phase(s). With further increasing the temperature or holding time, the SrTiO_3 phase formed from related intermediate phase(s), and the aligned crystallites were sintered to form dense SrTiO_3 with strong (001) orientation. The obtained SrTiO_3 microplatelets preserved the shape of SrBi_4Ti_4O_(15) and show high chemical and phase purity. This TMC mechanism has general applicability to a variety of compounds and will be very useful for the design and synthesis of novel anisotropic perovskite crystals with high quality in the future.