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DF: Fachverband Dielektrische Festkörper

DF 2: Nonlinear dielectrics, phase transitions, relaxors

DF 2.3: Talk

Monday, March 14, 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 Bismayer¹ — ¹Mineralogisch-Petrographisches Institut, Universität Hamburg — ²Faculty of Science, The Hebrew University of Jerusalem, Israel — ³Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria

Pb_0.78Ba_0.22Sc_0.5Ta_0.5O₃ (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.