Origin of the Large Field-Induced Strain and Enhanced Energy Storage Response of Rare-Earth-Doped Lead-Free 0.854BNT-0.12BKT-0.026BT Ceramics

Abstract

In this study, effects of rare-earth elements such as Nd, Gd, and Ce on the structural and electrical properties of lead-free bismuth sodium potassium barium titanate Bi0.487Na0.427K0.06Ba0.026TiO3 (0.854BNT-0.12BKT-0.026BT) (BNKBT) ceramics have been investigated in detail. Solid-state reaction method was used to prepare undoped, 1.0 mol% Nd, 1.0 mol% Gd, 1.0 mol%, 2.1 mol%, and 2.7 mol% Ce-doped BNKBT ceramic powder compositions. A pure single perovskite structure was observed in the X-ray diffraction (XRD) patterns for all the BNKBT ceramic systems, although doping was found to cause changes in peak splitting and peak positions due to their site preference. The Curie temperatures have not shifted significantly with doping, but the relative permittivity values were found to have increased. The nonergodic normal ferroelectric character of undoped BNKBT ceramic switched to an ergodic relaxor character at room temperature with Nd, Gd, and Ce doping with pinched polarization vs electric field hysteresis loops. Increased field-induced strain levels were observed in the doped BNKBT ceramics with 1 mole% Ce doping yielding a giant field-induced strain of 0.38% under an E-field of 65 kV/cm. Nd-doping, on the other hand, resulted in the highest releasable energy density of 0.64 J/cm(3) at 65 kV/cm. Consequently, the rare-earth-doped BNKBT ceramics were found to be promising for both digital actuator and high-energy-density capacitor applications due to their favorable electrical properties.