A new lead-potassium-free ceramic of (0.9-x)NaNbO3-0.1BaTiO(3)-xNaSbO(3) (NN-BT-xNS) was successfully prepared via a solid-state reaction method. The microstructure, phase structure, dielectric, ferroelectric, and piezoelectric properties were investigated as a function of NS content. The substitution of NS for NN was found to dramatically change the grain morphology from cube-like grains typical for alkaline niobate-based ceramics to conventional sphere-like grains especially for Pb-based perovskite ceramics. A normal to relaxor ferroelectric phase transformation was accompanied by a tetragonal (T) to rhombohedral (R) phase transition. A composition-temperature phase diagram demonstrated a vertical morphotropic phase boundary between T and R phases in the composition range of x=0.03-0.04, where optimum electrical properties of d(33)=252 pC/N, k(p)=36%, Q(m)=168, epsilon(T)(33)/epsilon(0)=2063, and T-c=109 degrees C were obtained in the x=0.035 ceramic sintered at 1260 degrees C. Particularly, excellent temperature insensitivity of small-signal piezoelectric properties suggested large application potentials in various actuators and sensors in comparison with other typical lead-free materials.