Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics with an excess Bi3+ and a deficiency of Na+ and K+ were synthesized by a conventional solid state reaction method. The structure and morphology ofBi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. The electric polarization and mechanical strain induced by external electric field, and the temperature dependence of dielectric constant were investigated. These results demonstrated that anergodic relax or phase can be induced by controls of the mole ratio of Bi3+, Na+ and K+. A phase boundary between non-ergodic and ergodic relaxor phases can be observed at ambient temperature. Theergodic relaxor phase can be transferred to the ferroelectric phase by application of the electric field. The stability of the induced ferroelectric phases strongly depends on the mole ratio of Bi3+, Na+ and K+. The maximum strain of 0.31% was observed in Bi0.51(Na0.78K0.22)0.47TiO3 ceramics sintered at 1,150℃ for 2 h.

The 0.99Bi0.5(Na0.78K0.22)0.5TiO3?0.01LaAlO3, 0.01LaMnO3 or 0.01LaFeO3 (0.99BNKT?0.01LA,0.01LM or 0.01LF) ceramics were prepared by a conventional mixed mothod. The structure andmorphology of the lead free ceramics were characterized by XRD (X-ray diffraction) and FE-SEM (fieldemission scanning electron microscopy). XRD results indicated that the BNKT ceramics modified by LA,LM or LF induced a transition from a ferroelectric tetragonal to a non-polar pseudo-cubic phase, leadingto decrease in the remnant polarization (Pr) and coercive field (Ec) in the P-E hysterisis loops. Theeffects of the BNKT ceramics modified by La-based ABO3 pervskite structure on the electric-fieldinduced strain were investigated, and the largest normalized unipolar strain (Smax/Emax) was found inBNKT-0.01LF ceramic.

0.935BaTiO3-0.065(Bi0.5Na0.5)TiO3+xmol%MnO2 (BBNTM-x) ceramics with 0≤x≤0.05 were fabricated with muffled sintering by a modified synthesis process. Their microstructure and enhanced positive temperature coefficient of resistivity (PTCR) characteristics were systematically investigated in order to obtain lead-free high TC PTCR thermistors. All specimens showed a perovskite structure with a tetragonal symmetry and no secondary phase was observed. Grain growth was achieved when the doped MnO2 was increased above 0.02 mol%. This is due to the effect of positive Mn ion doping as an acceptor compensating a Ba vacancy occurred by the higher donor dopant concentration of Bi3+ ion. Especially, enhanced PTCR characteristics of the extremely low ρRT of 99 Ω·㎝, PTCR jump of 5.1×10(3), α of 15.5%/℃ and high TC of 167℃ were achieved for the BBNTM-0.04 ceramics.

(1-x)BaTiO3-x(Bi0.5Na0.5)TiO3 (0.01≤x≤0.10) ceramics were fabricated with muffled sintering by a modified synthesis process. Their positive temperature coefficient of resistivity (PTCR) characteristics were investigated systematically. All specimen showed a perovskite structure with a tetragonal symmetry. Both the lattice parameter of a and c axes were slightly decreased with increasing (Bi0.5Na0.5)TiO3 (BNT) content. Grain growth was achieved when the incorporated BNT was increased to 6 mol% and the inhibition of grain growth is considered to be due to the appearance of Ba vacancy (V"(Ba)) in the (1-x)BaTiO3-x(Bi0.5Na0.5)TiO3 (0.08≤x). With 4 mol% BNT addition, room temperature resistivity decreased to 48 Ω·㎝ and a resistivity jump (ρmax/ρmin) was as high as 1.1×10(4), respectively. Curie temperature was also increased to 171˚C with increasing BNT content.