Structure–property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio. For Zr/Ti ratios of90/10and85/15,an incommensurate antiferroelectric state was found to be stabilized with increasing La content. Temperature-dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (&lgr;) was found to increase significantly with the decreasing Zr/Ti ratio and decreasing La content. The results of this study clearly demonstrate that the incommensurately modulated polar structures of PLZT are dependent on the relative antiferroelectric/ferroelectric phase stability, and the concentration of quenched La impurities. ©1997 American Institute of Physics.