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 The property of certain crystals that causes them to produce voltage when a mechanical pressure is applied to them such as sound vibrations. This technique is used to build crystal microphones, phonograph cartridges and strain gauges, all of which turn mechanical movement into voltage. 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 PMN abbr. polymorphonuclear leukocyte PMN polymorphonuclear neutrophil. PMN Polymorphonuclear leukocyte, see there ). When doped with sufficient [PbTiO.sub.3], a conventional ferroelectric, these disordered perovskites can exhibit strain levels up to one order of magnitude A change in quantity or volume as measured by the decimal point. For example, from tens to hundreds is one order of magnitude. Tens to thousands is two orders of magnitude; tens to millions is three orders of magnitude, etc. 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 mon·o·clin·ic adj. Of or relating to three unequal crystal axes, two of which intersect obliquely and are perpendicular to the third. monoclinic Adjective Crystallog 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 (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. Center for Neutron Research (NCNR NCNR NIST Center for Neutron Research NCNR Non-Cancelable, Non-Returnable NCNR National Center for Nursing Research (NIH) NCNR Nearest Common Node Rerouting (ATM) NCNR National Center for Neutron Research ) 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 A one-way direction of a signal or the molecules within a material pointing in one direction. 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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