Solid solution formation in the system (1-x) [(Na(0.5)K(0.5)NbO3)(0.93)-(LiTaO3)(0.07)]-x[BiScO3] has been investigated for compositions, 0 < x < 0.05. The tetragonal c/a ratio decreases with increasing BiScO3 content, with a discontinuity at x=0.02, X-ray diffraction patterns appear pseudo-cubic for x > 0.02. There is a 10-fold reduction in grain size between x=0.015 and x=0.02: dielectric peaks become suppressed and broadened at this point. Piezoelectric d(33) charge coefficients decrease across the compositional range. Results are discussed in terms of chemical inhomogeneity and grain-size effects.