The electric field-induced antiferroelectric-to-ferroelectric phase transition is investigated through detailed measurements of electric polarization P, longitudinal strain x₃₃, and transverse strain x₁₁ developed under applied electric fields in a series of Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_1−yTi_y]_0.98O₃ ceramics with compositions close to the antiferroelectric/ferroelectric phase boundary. It is found that the volume expansion, expressed as (x₃₃+2x₁₁), at the antiferroelectric-to-ferroelectric phase transition remains ∼0.4% regardless of the composition in the range of 0.060≤y≤0.075. However, the induced ferroelectric phase in compositions y≥0.069 becomes metastable and the ferroelectric-to-antiferroelectric phase transition does not occur during the unloading of the applied field. This reverse phase transition occurs partially when electric fields with reversed polarity are applied. As a consequence, the switchable mechanical strains in compositions y≥0.069 are significantly reduced as y (Ti content) increases even though the switchable polarization remains at a high value.