Effect of Co 2+ substitution in B-sites of the perovskite system on the phase formation, microstructure, electrical and magnetic properties of Bi 0.5 (Na 0.68 K 0.22 Li 0.10 ) 0.5 TiO 3 ceramics

Bi 0.5 (Na 0.68 K 0.22 Li 0.10 ) 0.5 Ti 1− x Co x O 3 lead-free perovskite ceramics (BNKLT− x Co, x = 0, 0.005, 0.010, 0.015 and 0.020) were fabricated via the solid-state combustion technique. A small-amount of Co 2+ 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 ( d * 33 ) of 460 pm·V −1 were achieved. The BNKLT−0Co ceramic showed diamagnetic behavior but all of the BNKLT− x Co ceramics exhibited paramagnetic behavior, measured at 50 K.