Effects of Rare Earth Doping on the Electrical and Electromechanical Properties of Lead-Free Bi0.487Na0.427K0.060Ba0.026TiO3 Ceramics

Abstract

In this study, the effect of 1.0 mole% Ce, Nd, and Gd doping on the dielectric, ferroelectric, and electromechanical properties of the bismuth sodium potassium barium titanate - BNKBT (Bi<inf>0.487</inf>Na<inf>0.427</inf>K<inf>0.060</inf>Ba<inf>0.026</inf>TiO<inf>3</inf>) lead-free ceramics have been studied in detail and compared with the undoped BNKBT samples. Ceramic samples have been synthesized by the conventional solid-state reaction method. XRD patterns revealed that all the BNKBT ceramic compositions show pure single perovskite phase. All of the BNKBT ceramics exhibited a dispersive dielectric behavior. The dielectric constant of undoped BNKBT ceramic was measured as 744 at 100 kHz at room temperature. The Curie temperature (T<inf>c</inf>) at 100 kHz was determined as 343°C. The dielectric constants were measured as 1249, 1326, and 1067 at 100 kHz at room temperature for Ce, Nd, and Gd doping, respectively. The Curie temperature (T<inf>c</inf>) at 100 kHz was determined as 343°C, 340°C, and 346°C, respectively. Addition of 1.0 mole% Ce, Nd, and Gd changed the polarization vs. electric field behavior of undoped BNKBT ceramic from a ferroelectric to an antiferroelectric character at room temperature. Maximum polarizations under 65 kV/cm applied electric field were measured as 40 ?C/cm2, 35 ?C/cm2, and 35 ?C/cm2and remnant polarizations were measured as 8.4 ?C/cm2, 6.7 ?C/cm2, and 12.3 ?C/cm2for Ce, Nd, and Gd doping, respectively, whereas these properties were measured as 39 ?C/cm2, and 33.1 ?C/cm2for undoped BNKBT. A large electric field-induced strain of 0.35%, 0.24%, and 0.23% was obtained under an electric field of 65 kV/cm as a result of field-induced phase change between antiferroelectric and ferroelectric phases, whereas the field-induced strain arising from piezoelectric effect in undoped BNKBT was 0.18%, with a piezoelectric coefficient (d<inf>33</inf>) of 165 pC/N. These results indicate that the BNKBT ceramics can be utilized in high energy density capacitor applications, as well as digital actuator applications. © 2020 Elsevier B.V., All rights reserved.