Synthesis and characterization of KTa0.55Nb0.45O3 modified Bi0.5Na0.5TiO3 lead-free Ferroelectric ceramic for energy storage applications

This study explores the synthesis and characterization of lead-free (1-x)(Bi_0.5Na_0.5TiO₃) – x(KTa_0.55Nb_0.45O₃) (BNT-KTN55) ceramics for their potential for practical energy storage applications, at an electric field < 50 kV/cm. The research addresses the challenge of optimizing relaxor ferroelectric behavior to exhibit a thin P-E loop at this practically relevant electric field. In the study, X-ray diffraction (XRD) and Rietveld refinement confirmed a coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases, with increasing tetragonal phase content as KTN55 doping increased. Scanning Electron Microscopy (SEM) revealed a significant reduction in grain size from 4.34 μm to 0.73 μm. Dielectric measurements showed typical relaxor ferroelectric behavior with frequency-dependent anomalies at T_s, T_m and a flat dielectric response in the range of 75° C to 310° C for higher doping levels. Ferroelectric measurements indicated a steady reduction in remnant polarization (P_r) and coercive field (E_c) with increasing KTN55 content. The composition with x = 0.06 demonstrated optimal performance, with a remnant polarization of 0.96 µC/cm², a maximum polarization of 14.42 µC/cm², and a discharge efficiency of 97.86% under a field of 43 kV/cm. The Recoverable energy density (W_rec) reached 0.295 J/cm³. All of the produced composite samples demonstrated stability without breakdown under the maximum applied electric field of 200 kV/cm, as limited by the instrument. Thus, their breakdown field exceeds this value, qualifying them as high breakdown field ceramics. These results suggest that BNT-KTN55 ceramics, particularly with x = 0.06, is a promising candidate for high-efficiency energy storage applications such as capacitors and pulse power devices.