Facile Glycothermal Synthesis of KxNa(1−x)NbO3 Particles

Abstract

KxNa(1−x)NbO3 particles (KNN, 0 < x < 1) were successfully synthesized through a facile glycothermal method by using KOH, NaOH and Nb2O5 as precursors and 1,4-butanediol as solvent at 200 °C for 12 h. The effects of varying the 1,4-butanediol/deionized water (B/W) volume ratio as solvent on the growth behavior, the morphological evolution, and the particle size of the synthesized KNN particles were investigated. In order to obtain K0.5Na0.5NbO3 with the morphotropic phase boundary (MPB) at the potassium content of x ≈ 0.5, the effect of varying K+/Na+ molar ratio on the composition of the obtained KNN particles was investigated. The crystal phase structure, morphology, particle size, chemical composition, and thermal behavior of the obtained particle samples were characterized using XRD, FE-SEM, EDS, TG, FT-IR, PSA, and TEM. The pure orthorhombic KNN particle close to NaNbO3 phase was obtained at the same concentration K+/Na+ of 1.0/1.0 and [K++Na+]/Nb molar ratio of 2.0/0.1. The synthesized K0.01Na0.99NbO3 particle exhibited a hexahedron shape with an average crystallite size of approximately 400 nm by glycothermal treated at 200 °C for 12 h. It is also demonstrated that the size of Na-rich KNN particles was decreased from 15 µm to 400 nm with increasing 1,4-butanediol content at various reaction conditions such as the volume ratio of B/W and can be controlled by 1,4-butanediol with an additive of water. Until the molar ratio of K+/Na+ reaches 1.6/0.4, the obtained particles have produced a Na-rich KNN phase, whereas when the molar ratio of K+/Na+ is 1.8/0.2, the particles could obtain a K-rich KNN phase. The results revealed that single-phase K0.5Na0.5NbO3 particles could be obtained at a relatively narrow molar ratio of K+/Na+ to 1.7/0.3. The particles with weakened agglomerate could obtain the average particle size of approximately 400 nm and a hexahedron shape. In comparison with the traditional hydrothermal method, the glycothermal method has been confirmed to be a more efficient method in controlling the particle size of KNN particles from micro- to sub-micron.