Structural, dielectric and ferroelectric properties of lead-free Na_0.5Bi_0.5TiO₃ ceramics prepared by spark plasma sintering technique

Lead-free Na_0.5Bi_0.5TiO₃ (NBT) fine-grained ceramics were prepared by spark plasma sintering method. Single phase ceramics with an ABO₃ perovskite structure were confirmed by X-ray diffraction method. The grain morphology was analyzed by using a scanning electron micrograph. The crystal particles arranged compactly and the typical grain size was about ≈200 nm. The depolarization temperature T_d, the rhombohedral–tetragonal phase transition temperature T_R−T and the temperature T_m of the maximum dielectric constant corresponding to tetragonal–cubic phase transition were determined to be 453 K, approximately 623 and 793 K, respectively, from the temperature dependence of dielectric properties. The P-E hysteresis loop at different temperatures indicated the existence of antiferroelectric state at the depolarization temperature T_d, which explained the antiferroelectric phase above T_d. The values of P_s, P_r and E_c reduced slightly with increasing temperature in the range 303–453 K