Studies of the structure-property relations of lead zirconate titanate (PZT) modified with lower valent substitutions on the A- and B-sites have been performed as a function of substituent concentration. These investigations have yielded common changes induced by these substitutions on ferroelectric phases. The commonalties are the presence of fine domains and polarization pinning effects. Differences in domain morphologies were observed between the rhombohedral and tetragonal ferroelectric phases. Rhombohedral ferroelectrics were found to exhibit 'wavy' domain patterns with increasing dopant concentrations, whereas a lenticular domain shape was preserved as the domain size was decreased for tetragonal ferroelectrics. These differences were explained in terms of different pinning mechanisms based on the differences in local elastic strain accommodations. Investigations of high Zr-content PZT have revealed that the ferroelectric rhombohedral phase becomes stabilized over the antiferroelectric orthorhombic with increasing concentrations of lower valent modifications. This change was explained in terms of the enhanced coupling between oxygen octahedra due to the bonding of oxygen-vacancy dipoles.