Near-room-temperature synthesis of niobate hydrate particles with hexagonal-platelike morphologies

Platelike alkaline niobates, which are an important class of templates for growing lead-free textured piezoceramic materials, are usually synthesized at temperatures greater than 900 °C from a melting process. We previously developed a hydrothermal route to niobate hydrate at temperatures above 100 °C and combined it with heat treatment to yield platelike niobate perovskite. In this contribution, we present the first report on near-room-temperature wet-chemical preparation of platelike potassium niobate (KN) and potassium sodium niobate (KNN) hydrate particles. Hexagonal-platelike KN-hydrate particles that were 1.5-4.0 μm wide and 0.1-0.35 μm thick were prepared via low temperature synthesis at 60 °C over a period of 24 h in a 9 mol/L KOH solution. Similarly, KNN hydrate particles with a hexagonal-platelike shape were prepared at 40 °C over a period of 48 h in 6 mol/L [OH−]. Sodium dodecyl benzene sulfonate (SDBS) surfactant was added as a shape modulator. Calcining the KN hydrate particles at 500 °C for 2 h transformed the crystals to a stable perovskite phase while maintaining the platelike morphology. The low-temperature wet-chemical route to alkaline niobates is expected to lead to a low-cost scalable method for the mass production of platelike template particles in the field of high-performance lead-free piezoceramics.