AN INCOMMENSURATE-COMMENSURATE PHASE-TRANSFORMATION IN ANTIFERROELECTRIC TIN-MODIFIED LEAD-ZIRCONATE-TITANATE

Antiferroelectric tin-modified lead zirconate titanate ceramics (PZST), with 42 at.% Sn and 4 at.% Ti, were studied by hot- and cold-stage transmission electron microscopy and selected area electron diffraction techniques. The previously reported tetragonal antiferroelectric state is shown to be an incommensurate orthohombic state. Observations revealed the existence of incommensurate 1/x <110> superlattice reflections below the temperature of the dielectric maximum. The modulation wavelength for this incommensurate structure was found to be metastably locked-in near and below room temperature. An incommensurate-commensurate orthorhombic antiferroelectric transformation was then observed at lower temperatures. However, an intermediate condition was observed over a relatively wide temperature range which was characterized by an intergrowth of <110> structural modulations, which was strongly diffuse along the <110>. These structural observations were correlated with dispersion in the dielectric properties in the same temperature range. No previous reports of an incommensurate orthorhombic antiferroelectric state or an incommensurate-commensurate orthorhombic antiferroelectric transformation are known to exist.