Dresden 2006 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 3: Poster Session

DF 3.25: Poster

Montag, 27. März 2006, 09:30–17:00, P1

Temperature evolution of the phonon anomalies in relaxor ferroelectic PbSc_0.5(Nb,Ta)_0.5O₃ — •Boriana Mihailova¹, Ulrich Bismayer¹, Bernd Güttler², Rainer Stosch², and Marin Gospodinov³ — ¹Mineralogisch-Petrographisches Institut, Universität Hamburg, Grindelallee 48, D-20146 Hamburg, Germany — ²Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany — ³Institute of Solid State Physics - Bulgarian Academy of Sciences, Blvd. Tzarigradsko Chausee 72, 1784 Sofia, Bulgaria

Single crystals of stoichiometric PbSc_0.5Ta_0.5O₃ (PST) and PbSc_0.5Nb_0.5O₃ (PSN) as well as mixed PbSc_0.5(Nb_xTa_1−x)_0.5O₃ compounds are investigated by Raman scattering and X-ray diffraction. The temperature dependence of the polarized Raman spectra reveals different preferred ferroic species in PST and PSN. Near the dielectric constant maximum cooperative shifts of Pb atoms in respect to the oxygen sheets perpendicular to the cubic body diagonal occur in larger spatial regions for PST than for PSN. On cooling down this structural modification becomes preferential for PST, thus giving rise to highly anisotropic ferroelectric domains. In PSN the temperature decrease favours B-cation deviations from the BO₆-octahedral centres, which leads to formation of small-sized polar clusters distributed in the isotropic matrix. Near 180 K PST undergoes an additional phase transition, which involves reduction of the rotation symmetry. The loading of Nb into PST affects strongly the nanoscale domain texture and the structural transformations that occur on cooling down.