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The polar nanostructure of novel relaxor ferroelectric materials. (News Briefs).

A renaissance in the field of ferroelectricity has taken place over the past several years ever since the finding of exceptional piezoelectric properties in the lead-oxide class of relaxor ferroelectric materials Pb([Zn.sub.1/3][Nb.sub.2/3])[O.sub.3] (PZN) and Pb([Mg.sub.1/3][Nb.sub.2/3])[O.sub.3] (PMN). When doped with sufficient [PbTiO.sub.3], a conventional ferroelectric, these disordered perovskites can exhibit strain levels up to one order of magnitude higher than those attained using present day industrial PZT ceramics, making them highly promising candidates for the next generation of solid-state transducers and actuators. Part of this novel behavior has been attributed to the presence of a narrow monoclinic region in the phase diagrams for solid solutions of both PZN and PMN doped with [PbTiO.sub.3], But as even the undoped compounds exhibit a superior piezoelectric character, the underlying polar nanostructure, absent in [PbTiO.sub.3], is believed to play an essential role in these materials.

Scientists at the NIST Center for Neutron Research (NCNR) and Brookhaven National Lab have an ongoing collaborative program to study the lattice dynamics (atomic vibrations) in the PZN and PMN relaxor compounds. Recent neutron inelastic scattering measurements at the NCNR have demonstrated a direct relationship between the lowest-frequency transverse optical lattice vibration and the polar nanostructure, thereby resolving a long-standing discrepancy between prior x-ray and neutron results. In PMN this vibrational mode becomes overdamped at 620 K, which is the same temperature at which the polarized nanometer-scale domains begin to develop. Concurrently, an unusual broadening of the transverse acoustic vibrational mode begins at 620 K, and increases strongly with decreasing temperature. These results indicate that this optical lattice vibration condenses into the polar nanoregions, resulting in a non-uniform distortion of the crystal lattice.

Subsequent experiments to clarify further how the polar nanoregions are responsible for the novel piezoelectricity observed in these and other relaxor systems are underway.

CONTACT: Peter Gehring, (301) 975-3946; peter. gehring@nist.gov.
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Publication:Journal of Research of the National Institute of Standards and Technology
Article Type:Brief Article
Geographic Code:1USA
Date:Mar 1, 2002
Words:334
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