The effect of LaFeO3 addition to Bi1/2(Na0.78K0.22)1/2TiO3 ceramics on the phase stability and macroscopic functional properties was investigated. Similarly to other chemical modifiers known in the literature, LaFeO3 addition suppresses an electric-field-induced long-range ferroelectric order, giving rise to a giant unipolar strain of ∼0.3% at 2 mol% LaFeO3 addition. Time-dependent changes in polarization and strain hysteresis loops both during successive electrical cycling and after removal of the electric field suggest that a specimen with 2 mol% LaFeO3 consists of both ergodic and nonergodic phases, which is unique among the known relaxor materials.