Synthesis of KCa₂Nb₃O₁₀ Crystals with Varying Grain Sizes and Their Nanosheet Monolayer Films As Seed Layers for PiezoMEMS Applications

The layered perovskite-type niobate KCa₂Nb₃O₁₀ and its derivatives show advantages in several fields, such as templated film growth and (photo)catalysis. Conventional synthesis routes generally yield crystal size smaller than 2 μm. We report a flux synthesis method to obtain KCa₂Nb₃O₁₀ crystals with significantly larger sizes. By using different flux materials (K₂SO₄ and K₂MoO₄), crystals with average sizes of 8 and 20 μm, respectively, were obtained. The KCa₂Nb₃O₁₀ crystals from K₂SO₄ and K₂MoO₄ assisted synthesis were protonated and exfoliated into monolayer nanosheets, and the optimal exfoliation conditions were determined. Using pulsed laser deposition, highly (001)-oriented piezoelectric stacks (SrRuO₃/PbZr_0.52Ti_0.48O₃/SrRuO₃, SRO/PZT/SRO) were deposited onto Langmuir-Blodgett films of Ca₂Nb₃O₁₀^- (CNO) nanosheets with varying lateral nanosheet sizes on Si substrates. The resulting PZT thin films showed high crystallinity irrespective of nanosheet size. The small sized nanosheets yielded a high longitudinal piezoelectric coefficient d₃₃ of 100 pm/V, while the larger sized sheets had a d₃₃ of 72 pm/V. An enhanced transverse piezoelectric coefficient d₃₁ of -107 pm/V, an important input parameter for the actuation of active structures in microelectromechanical systems (MEMS) devices, was obtained for PZT films grown on CNO nanosheets with large lateral size, while the corresponding value on small sized sheets was -96 pm/V.