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Dresden 2011 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 2: Nonlinear dielectrics, phase transitions, relaxors

DF 2.3: Vortrag

Montag, 14. März 2011, 11:40–12:00, KÖN Farb

Structural transformations in relaxor ferroelectrics on the mesoscopic scale — •Bernd J. Maier1, Boriana Mihailova1, Evgeniy A. Dul’kin2, Tim Prüßmann1, Carsten Paulmann1, Marin Gospodinov3, and Ulrich Bismayer11Mineralogisch-Petrographisches Institut, Universität Hamburg — 2Faculty of Science, The Hebrew University of Jerusalem, Israel — 3Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria

Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) is a canonical relaxor, undergoing on cooling a series of structural transformations without developing long-range ferroelectric order. Recently, it has been established that perovskite-type relaxors exhibit a characteristic temperature T, at which initially formed polar clusters slow down and merge into larger polar nanoregions (PNRs). For PBST the temperature T is near 490 K as revealed by Raman scattering (RS) and acoustic emission (AE). RS data indicate that the transformation processes near T are realized via coupling of off-centred octahedral cations from adjacent polar clusters. AE experiments reveal that the coupling is highly anisotropic and is strongest along ⟨110⟩ cubic directions. AE measurements also demonstrate a temperature hysteresis of ∼15 K. Since PNRs generate strong x-ray diffuse scattering (XDS) along the ⟨110⟩ directions, the XDS intensity was used as an order parameter to determine the thermodynamical character of the phase transformation occurring at T. The temperature evolution of XDS in PBST measured with synchrotron radiation reveals a near-tricritical behaviour in terms of the Landau theory.

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