Role of alkali carbonate and salt in topochemical synthesis of K_1/2Na_1/2NbO₃ and NaNbO₃ templates

Abstract

Since the properties of lead-free piezoelectric materials have thus far failed to meet those of lead-based materials, either chemical doping or morphological texturing should be employed to improve the piezoelectric properties of lead-free piezoelectric ceramics. The goal of this study was to synthesize plate-like K_1/2Na_1/2NbO₃ and NaNbO₃ particles, which are the most favorable templates for morphological texturing of K_1/2Na_1/2NbO₃ ceramics. To achieve this goal, Bi_2.5Na_3.5Nb₅O₁₈ precursors in a plate-like shape were first synthesized and subsequently converted into K_1/2Na_1/2NbO₃ or NaNbO₃ particles that retain the morphology of Bi_2.5Na_3.5Nb₅O₁₈. In this study, we found that sodium or potassium carbonate does not play a major role in converting the Bi_2.5Na_3.5Nb₅O₁₈ precursor to K_1/2Na_1/2NbO₃ or NaNbO₃, on the contrary to previous reports; however, the salt contributes to the conversion reaction. All synthesis processes have been performed via a molten salt method, and scanning electron microscopy, scanning probe microscopy, and inductively coupled plasma mass spectroscopy were used to characterize the synthesized K_1/2Na_1/2NbO₃ or NaNbO₃ templates.