Data are reported for the dielectric, piezoelectric, electrostrictive, and ferroelectric properties of potassium-substituted sodium bismuth titanate, [(K(x)Na(1-x))(0.5)Bi(0.5)]TiO3. For the morphotropic phase boundary composition x = 0.2, relaxor-type behavior was observed at room temperature with piezoelectric (effective d(333) = 325 x 10(-12) m/V) and ferroelectric properties (P(R) = 25 microC/cm(2), E(C) = 30 kV/cm). A transition to a relatively frequency-independent, diffuse phase transformation region occurred with increasing temperature, with no remanent strain or coercive field. Above the transition temperature, the field-induced strain was consistent with contributions from electrostriction and field induced piezoelectricity (M(3333) = 1.9 x 10(-16) m2/V2 and d333 = 81 x 10(-12) m/V at 100 degrees C). Information is given for the temperature dependence of properties, e.g., 0.14% strain induced at 50 kV/cm at 200 degrees C. Higher potassium content x = 0.6 stabilized the ferroelectric piezoelectric region to temperatures above 200 degrees C, with a relatively stable d(333) = 150-145 x 10-12 m/V between 25 degrees C and 200 degrees C. Pb-free KNBT ceramics appear competitive with PZT, especially for higher temperature electromechanical applications.