Phase Transition and Ferroelectric Properties of KNN- BiScO3 Ferroelectric System

Abstract

Piezoelectric materials are a class of dielectric material which have the ability to convert mechanical stress into electric signals and vice-versa. The harmful nature of traditional lead-based ceramics has intensified efforts to discover viable lead-free alternatives. Out of numerous lead-free materials, Potassium Sodium Niobate (K0.5Na0.5NbO3(KNN)) stands most promising because of its high Curie temperature (420°C) and significant ferroelectric and dielectric properties showing implicit applications in piezoelectric sensors, actuators, high-temp capacitor applications, energy-harvesting devices etc.1 Besides, it has associated problems like the hygroscopic nature of constituent alkali components which renders its physical properties sensitive to atmospheric conditions. Its moderate electromechanical properties, tendency of abnormal grain growth and narrow range of sintering temperature are issues of concern.2 In order to overcome the above issues, many strategies have been taken into considerations e.g. addition of sintering aid, hot-plasma sintering, micro-wave sintering, spark-plasma sintering, chemical substitution and fabrication of solid solutions. Among these approaches, the fabrication of solid solutions, being the most effective one has been employed in this work. In the present study, we have synthesized the ferroelectric solid solution of KNN and BiScO3. Bi3+ is isoelectronic with Pb 2+ which can hybridize with O2- to produce a lone pair leading to enhancement of piezoelectricity and other functional properties.3 The ferroelectric solid solutions with chemical formula: (1-x) K0.5Na0.5NbO3-xBiScO3, where x = 0.000, 0.005, 0.010, 0.015, 0.020, 0.030, 0.040, 0.050 are synthesized via conventional solid-state reaction method. A combination of X-ray powder diffraction (XRPD), SEM micrographs, Raman spectroscopy, and temperature-dependent dielectric and piezoelectric measurements were employed to gather data across diverse experimental conditions. XRPD patterns have confirmed the crystallization of the ceramic solid solution in a perovskite phase. Raman scattering spectra and Rietveld refinement analysis of the XRPD data provides deep down insights into the phase transitions driven by composition. Temperature dependent dielectric properties dielectric constant (r) and dielectric loss (tan ) at various frequencies offers perspective on the ferroelectric phase transition behaviour. The piezoelectric coefficient (d33) for KNN has been significantly enhanced, with a maximum value of 154 pC/N at x = 0.015, highlighting the effectiveness of BiScO3 in enhancing piezoelectric properties.