Prior studies have shown that a field-induced ferroelectricity in ceramics with general chemical formula (1-x-y)( Bi _1/2 Na _1/2) TiO ₃–x BaTiO ₃–y( K _0.5 Na _0.5) NbO ₃ and a very low remanent strain can produce very large piezoelectric strains. Here we show that both the longitudinal and transverse strains gradually change with applied electric fields even during the transition from the nonferroelectric to the ferroelectric state, in contrast to known Pb-containing antiferroelectrics. Hence, the volume change and, in turn, the phase transition can be affected using uniaxial compressive stresses, and the effect on ferroelectricity can thus be assessed. It is found that the 0.94( Bi _1/2 Na _1/2) TiO ₃–0.05 BaTiO ₃–0.01( K _0.5 Na _0.5) NbO ₃ ceramic (largely ferroelectric), with a rhombohedral R3c symmetry, displays large ferroelectric domains, significant ferroelastic deformation, and large remanent electrical polarizations even at a 250 MPa compressive stress. In comparison, the 0.91( Bi _1/2 Na _1/2) TiO ₃–0.07 BaTiO ₃–0.02( K _0.5 Na _0.5) NbO ₃ ceramic (largely nonferroelectric) possesses characteristics of a relaxor ferroelectric ceramic, including a pseudocubic structure, limited ferroelastic deformation, and low remanent polarization. The results are discussed with respect of the proposed antiferroelectric nature of the nonferroelectric state.