Composition-induced antiferroelectric phase and giant strain in lead-free (Na_y,Bi_z)Ti_1-xO_3(1-x)-xBaTiO ₃ ceramics

(Na_y,Bi_z)Ti_1-xO_3(1-x)- xBaTiO₃ ceramics with an excess in Bi3⁺ and/or a deficiency in Na⁺ were prepared and investigated. It is found that an antiferroelectric phase can be induced through a modulation of the mole ratio of Na⁺ and Bi3⁺. A phase boundary between ferroelectric and antiferroelectric phases can be observed at ambient temperature. A modulated phase, which is the origin of relaxor antiferroelectric behavior, should be attributed to a compositional modulation. The antiferroelectric phase can be induced to the ferroelectric phase by an applied electric field. The stability of the induced ferroelectric phase strongly depends on the mole ratio of Na ⁺ and Bi3⁺. A recoverable giant strain of 0.48% comparable to PbZrO₃-based antiferroelectrics as well as electrostrictive coefficients (0.026 C4m^-2) much higher than lead-based relaxor ferroelectrics with low-temperature dependence was achieved in (Na _y,Bi_z)Ti_1-xO_3(1-x)-xBaTiO ₃ antiferroelectrics. Our results show there is a high possibility that the novel lead-free antiferroelectrics will replace the PbZrO ₃-based ones.