Effect of Na non-stoichiometry in Sr(Hf0.5Zr0.5)O-3-modified Bi-0.5(Na(0.8+x)K0.2)(0.5)TiO(3)ceramics was examined in the range of - 0.04 <= x <= 0.04. The effect of Na non-stoichiometry on microstructure, ferroelectric, piezoelectric, dielectric properties and high-temperature impedance was explored. Compared to the stoichiometric compositions, Na excess and deficiency exhibit the same effect as observed for the acceptor and donor doping, respectively. All non-stoichiometric and stoichiometric compositions exhibit a pure ABO(3)perovskite phase with pseudocubic symmetry. The deficiency of Na in ceramics decreases the grain size and drives the system towards ergodic relaxor as evident by pinched ferroelectric loop and the negligible negative strain along with an increase in maximum strain (S-m). The corresponding normalized strain (S-m/E-max.) increased from 275 to 800 pm/V when Na content decreased from x = + 0.04 to - 0.04. In contrast, excess Na exhibits the converse effect and drives the system towards ferroelectricity. Composition with deficient Na also exhibits lower dielectric loss and increase in resistivity by an order of magnitude compared to excess Na as observed from the high-temperature dielectric and impedance measurements. The results of this study demonstrate that Na non-stoichiometry significantly affects the electric properties of the studied system and thus can be effectively modulated to achieve improved electromechanical properties for materials having actuator-based applications.