Thursday, December 8, 2005, 1:30 pm — Small seminar room, Bldg. 510
The competition and coexistence of local short-range and long-range polar order underlie the behaviour of relaxor ferroelectrics, materials of considerable technological importance. The conventional picture is that the polar nano-regions (PNR) that appear at high temperature form nuclei for the field-induced long-range order at low temperature. Here I will discuss neutron and high-energy-x-ray diffuse scattering measurements on
relaxor systems Pb(Zn1/3Nb2/3)O3 (PZN) and Pb(Mg1/3Nb2/3)O3 (PMN), that probe directly the shape and polarization of the PNR. A very unusual configuration was revealed with applying a electric field on PZN along the [111] direction. Contrary to conventional expectations, the overall diffuse scattering intensity is not suppressed, even in a field as high as
40 kV/cm. On the other hand, the field induces a dramatic change on the shape of the three-dimensional diffuse scattering intensity pattern in reciprocal space, corresponding to a redistribution of PNR in real space.
These surprising results are consistent with a model in which the PNR with <110>-type polarizations, orthogonal to that of the surrounding environment, are embedded and persist in the [111]-polarized ferroelectric order of the bulk.
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