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 t ransmission electron microscopy and selected area electron diffraction techniques. The previously reported tetragonal antiferroelectric stat e is shown to be an incommensurate orthohombic state. Observations rev ealed the existence of incommensurate 1/x <110> superlattice reflectio ns below the temperature of the dielectric maximum. The modulation wav elength for this incommensurate structure was found to be metastably l ocked-in near and below room temperature. An incommensurate-commensura te orthorhombic antiferroelectric transformation was then observed at lower temperatures. However, an intermediate condition was observed ov er a relatively wide temperature range which was characterized by an i ntergrowth of <110> structural modulations, which was strongly diffuse along the <110>. These structural observations were correlated with d ispersion in the dielectric properties in the same temperature range. No previous reports of an incommensurate orthorhombic antiferroelectri c state or an incommensurate-commensurate orthorhombic antiferroelectr ic transformation are known to exist.