Studies of the structure-property relationships have been performed for lead zirconate titanate as a function of concentration of a lower-valent A-site substitution. Investigations focused on the system (Pb1-yKy)(Zr0.65Ti0.35)O 3-y/2 for 0<y<0.20. These studies revealed modest changes in the dielectric response with increasing K1+ concentration. However, no evidence of relaxor ferroelectric characteristics was found. Transmission electron microscopy (TEM) studies were also performed. These investigations revealed strong changes in the ferroelectric domain structures with moderate increases in K1+ concentration. For K content >4%, fine ferroelectric domains were found, which possessed a strong degree of wavy character. Increasing K1+ concentration resulted in further decreases in domain size. Sawyer-Tower polarization studies then demonstrated a strong reduction in the switchable polarization with increasing K1+ concentration, indicating that the polarization becomes pinned. Hot-stage TEM investigations were then performed. These studies revealed evidence for a pinning of the polarization into fine wavy domains at temperatures significantly below that of the ferroelectric transformation. These results are then compared to recent investigations of the influence of La3+ on the same base composition. We believe that the differences between lower- (K1+) and higher- (La3+) valent A-site modifications can be explained on the basis of the influence of quenched (which become mobile on heating in the ferroelectric phase) versus randomly quenched (above the ferroelectric transformation) defect complexes on the evolution of polar order.