The role of Fe as an acceptor and Nb as a donor in [0.94−x](Bi1/2Na1/2)TiO3–0.06BaTiO3−x (K0.5Na0.5)NbO3 (100xKNN) (x = 0.02 and 0.03) lead-free piezoceramics was investigated. X-ray diffraction analyses show that all the profiles are best-fitted with a cubic symmetry where Fe doping tends to induce a lattice expansion, while Nb doping does the opposite. The strain and polarization characteristics are enhanced and suppressed by the acceptor and donor dopants, respectively. The improvement in the electrical properties with acceptor doping is accompanied by the stabilization of a ferroelectric order. Electron paramagnetic resonance spectroscopic analysis suggests that the stabilization of the ferroelectric order by the Fe dopant originates from the formation of (FeTi′–VO••)• defect dipoles.