Flux growth of lead free (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3 ferroelectric single crystals and their characterization

Abstract

We have grown single crystals of lead-free (Na_0.5Bi_0.5)TiO₃–(K_0.5Bi_0.5)TiO₃ (abbreviated as BNKT) as promising materials for ferroelectric applications. The single crystals were grown by a high temperature self-flux solution method in which A-site compounds were used as complex flux. The crystal structure was analyzed by means of an X-ray diffraction technique showing a perovskite phase with tetragonal symmetry at room temperature. The surface morphology of the BNKT crystals was examined by scanning electron microscopy (SEM) and was found depicting a layered like hopper structure. The temperature and frequency dependence of the dielectric constant and loss for the as-grown single crystals was investigated, showing a decrease in T_max from 316 °C at 50 kHz to 310 °C at 1 MHz. To study the degree of dielectric relaxation, modified power law fitting and Lorentz type quadratic fitting were performed. The relative composition of the studied sample and its phase transition behavior were confirmed by Raman spectroscopy. The piezoelectric coefficient d₃₃ with optimized poling field was found to be 216 pC N⁻¹. The ferroelectric response of the BNKT crystals with temperature at an applied field of 37 kV cm⁻¹ was studied. The results suggest a promising approach for growing high quality alkali based single crystals with a relatively large size for piezoelectric and ferroelectric applications.