Effect of Co²⁺ substitution in B-sites of the perovskite system on the phase formation, microstructure, electrical and magnetic properties of Bi_0.5(Na_0.68K_0.22Li_0.10)_0.5TiO₃ ceramics

Bi_0.5(Na_0.68K_0.22Li_0.10)_0.5Ti_1–xCo_xO₃ lead-free perovskite ceramics (BNKLT–xCo, x = 0, 0.005, 0.010, 0.015 and 0.020) were fabricated via the solid-state combustion technique. A small-amount of Co²⁺ ion substitution into Ti-sites led to modification of the phase formation, microstructure, electrical and magnetic properties of BNKLT ceramics. Coexisting rhombohedral and tetragonal phases were observed in all samples using the X-ray diffraction (XRD) technique. The Rietveld refinement revealed that the rhombohedral phase increased from 39% to 88% when x increased from 0 to 0.020. The average grain size increased when x increased. With increasing x, more oxygen vacancies were generated, leading to asymmetry in the bipolar strain (S–E) hysteresis loops. For the composition of x = 0.010, a high dielectric constant (ε_m) of 5384 and a large strain (S_max) of 0.23% with the normalized strain \left(d_33^*\right) of 460 pm·V^–1 were achieved. The BNKLT–0Co ceramic showed diamagnetic behavior but all of the BNKLT–xCo ceramics exhibited paramagnetic behavior, measured at 50 K.