Synthesis and formation mechanisms of high aspect ratio platelike NaNbO₃ particles by topochemical microcrystal conversion

High aspect ratio platelike sodium niobate (NaNbO₃) was successfully synthesized from precursor Bi_2.5Na_3.5Nb₅O₁₈ by the topochemical microcrystal conversion process. Platelike bismuth layered-perovskite Bi_2.5Na_3.5Nb₅O₁₈ precursor was first synthesized by the molten-salt synthesis process, and then reacted with the complementary reactant Na₂CO₃ in NaCl flux, the platelike Bi_2.5Na_3.5Nb₅O₁₈ particles were transformed into the perovskite NaNbO₃ particles that preserved the morphology of Bi_2.5Na_3.5Nb₅O₁₈ precursor at 950 °C for 4 h with the weight ratio of oxide to salt 1:1.5. The length of NaNbO₃ seed crystals was in the range of 15-30 μm, and the thickness range was 0.6-1 μm. The aspect ratio of length to thickness varied from 15:1 to 50:1. Furthermore, by surveying the variations of the crystal micrographs and X-ray diffraction patterns, formation mechanisms were proposed from changing soaking temperature, salt amount and soaking time in the process.