Ferroelectric Properties of Lead-free Non-stoichiometric Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 Ceramics for Energy Conversion

In order to create A-site vacancy, lead-free Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics were synthesized by a conventional solid state reaction method. In this paper, we investigated the dielectric and electrical properties of Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics with an excess Bi3+and a deficiency of Na+ and K+. The structure and morphology of Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. Also the temperature dependent dielectric constant and loss and the electric field dependent polarization and strain were measured. From these results, it is found that an antiferroelectric phase can be induced through a modulation of the mole ratio of Bi3+, Na+ and K+. A phase boundary between ferroelectric and antiferroelectric phases can be observed at ambient temperature. The antiferroelectric phase can be induced to the ferroelectric phase by an applied electric field. The stability of the induced ferroelectric phases strongly depends on the mole ratio of Bi3+, Na+ and K+. A recoverable strain of 0.33% was achieved in Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics.