A thermodynamic study of phase transitions and electrocaloric properties of K0.5Na0.5NbO3 single crystals

Lead-free ferroelectrics K1-xNaxNbO3 are promising candidates for sensors and electromechanical and cooling devices. Here, we study the thermodynamics of phase transitions and electrocaloric (EC) properties of K0.5Na0.5NbO3 single crystals subject to electric, thermal, and mechanical stimuli, from which we establish the temperature-pressure and temperature-electric field phase diagrams. The focus is on understanding the pressure effect on the ferroelectric properties of K1-xNaxNbO3, which is critical to develop chemical doping strategies to achieve targeted performances via chemical strain engineering. Under pressure-free conditions, the K0.5Na0.5NbO3 single crystal has a Curie temperature of around 673K, which is the optimal operating temperature for the EC effect. We show that a hydrostatic pressure of around 7GPa can reduce the optimal operating temperature to near room temperature, 300K, at the expense of decreasing the EC temperature change Delta T-EC from 5.4K to 2.4K when the applied electric field is 10MV/m. The present work provides a fundamental understanding of the pressure-induced phase transitions and ferroelectric properties and can be employed to guide the future design of K1-xNaxNbO3-based materials. Published under license by AIP Publishing.