Micro-morphology and dielectric properties for (K0.45Na0.55)NbO3 lead-free piezoelectric crystal

Abstract

Lead-free piezoelectric 〈001〉-oriented KNN crystals each with a dimension of 5 mm3 mm1 mm are obtained by melt grown technique. The room temperature crystal structure of orthorhombic perovskite-type lattice is determined from XRD measurment. The SEM observation reveals the growth steps aligning approximately along the [001] direction. Base on the model of negative ion coordination polyhedrons, it is explained that the layer growth mechanism is dominant for the 〈001〉 face. Two phase transition temperatures of orthorhombic-to-tetragonal (O-to-T) and tetragonal-to-cubic (T-to-C) are around 240 ℃ and 405 ℃ for KNN crystals according to the dielectric measurements, respectively. A linear fitting of the modified Curie-Weiss law to experimental data shows that the normal ferroelectric property is dominant for KNN crystal.