Incommensuration in La-modified antiferroelectric lead zirconate titanate ceramics

Lanthanum-modified lead zirconate titanate (PLZT) specimens with a La content of 2 at. % and a Zr/Ti ratio of 95/5 (PLZT 2/95/5) have been investigated by dielectric spectroscopy, Sawyer–Tower polarization (P-E) measurements, and hot-stage transmission electron microscopy (TEM). La ‘‘impurities’’ have been found to induce a 1/x〈110〉 incommensurate antiferroelectric structure at about 210 °C from a ferroelectric structure when cooled from above. The incommensurate structure was found to be stable below this temperature of the dielectric maximum, evolving slowly with decreasing temperature towards the commensurate antiferroelectric orthorhombic PZ structure. The incommensuration is believed to arise due to a competition between ‘‘broken’’ dipolar (ferroelectric) and sublattice (antiferroelectric) interactions. The ‘‘dirty’’ antiferroelectric Pb-based system may be the first example of a proper incommensurately displacively modulated ferroelectric-type material.