An incommensurate-commensurate phase transformation in antiferroelectric tin-modified lead zirconate titanate
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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 l/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.
I. INTRODUCTION Tin-modified lead zirconate titanate ceramics, Pb(0.98) Nb0.02[(Zri-x,Snx)1_3,Ti>,]098O3 (designated as PZST x/ y/2), are of interest as potential actuator and transducer materials. In this crystalline solution series, a fieldinduced antiferroelectric to ferroelectric phase transformation occurs. Associated with this transformation are large nonlinearities in the dielectric, electromechanical, and thermal mechanical response characteristics.1 Shape changes as large as 1% were reported for field-stabilization of the ferroelectric phase.1 Jaffe et al. were the first to report on this crystalline solution series.2 A comprehensive study of the effects of chemical modifications on the relative phase stabilities followed.3 More recently a systematic study of the effects of temperature, pressure, and grain size on the field-induced antiferroelectric to ferroelectric transformation characteristics was carried out by Yang and Payne.4'5 A complex phase sequence was previously reported for the compositional region 0.40 < x < 0.50 and 0 < y < 0.10.3'4 On cooling, transformations from single-cell cubic, to multicell cubic, and tetragonal antiferroelectric were deduced from dielectric and structural investigations. A lower temperature transition to either a rhombohedral ferroelectric or an orthohombic antiferroelectric is known to occur which is dependent on Ti content.3'4 High Ti-content specimens (x > 0.06) transform to a rhombohedral ferroelectric state, whereas low Ti-content compositions (x < 0.05) transform to an J. Mater. Res., Vol. 10, No. 2, Feb 1995 http://journals.cambridge.org
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orthorhombic antiferroelectric state.4'5 Strong dielectric anomalies are not observed at the ferroelectric-antiferroelectric, or antiferroelectric-multicell cubic transformations. The maximum die
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