Impurity-induced incommensuration in antiferroelectric La-modified lead zirconate titanate.

Abstract

Lanthanum-modified lead zirconate titanate (PLZT) specimens with La contents x between 0 and 5 at. % and a Zr/Ti ratio of 95/5 (PLZT x/95/5) have been investigated by dielectric spectroscopy, Sawyer-Tower polarization (P-E) measurements, and hot-stage transmission electron microscopy (TEM). The dominate phase of PLZT 0/95/5 was found to be isostructural with that of the high-temperature phase of ${\mathrm{PbZrO}}_{3}$ (\ensuremath{\sim}230 \ifmmode^\circ\else\textdegree\fi{}C), which is known to be characterized by the presence of 1/2〈110〉 superlattice reflections. An antiferroelectric state was found to be stabilized as the long-range ferroelectric state was disrupted by a small amount of La substitution on the Pb sites. With increasing La content, the antiferroelectric-paraelectric transformation was found to proceed through an incommensurate region. (1/x)〈110〉 incommensurate reflections were observed in selected area electron diffraction (SAED) patterns on cooling below the temperature of the dielectric maximum (${\mathit{T}}_{\mathrm{max}}$) for PLZT 2/95/5 and 5/95/5. A diffuse incommensurate-commensurate transformation was observed at lower temperatures. It is proposed that incommensuration in antiferroelectric PZT is induced by La impurity content. The incommensuration is believed to arise due to a competition between broken dipolar and antiferroelectric sublattice interactions. A possible transformational sequence is, then, suggested for inhomogeneous antiferroelectrics.