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DF: Fachverband Dielektrische Festkörper

DF 3: Relaxor Ferroelectrics

DF 3.1: Hauptvortrag

Montag, 26. März 2007, 14:30–15:10, H11

Investigation of relaxor ferroelectrics by piezoresponse force microscopy — •Vladimir Shvartsman and Wolfgang Kleemann — Angewandte Physik, Universität Duisburg-Essen, D-47048 Duisburg, Germany

Relaxor ferroelectrics (relaxors) belong to a special group of polar oxides. In contrast to normal ferroelectrics, dynamic polar nanometer-sized regions (PNRs) appear in these materials deep in the nominally paraelectric state. On cooling a transition either into a short-range ordered clusterglass-like state or into a long-range ordered domain state occurs. In spite of numerous intense investigations the information about the evolution of the PNRs, in particular in the vicinity of the transition temperature, is still insufficient. New information about the polar structure of relaxors may be obtained by piezoresponse force microscopy (PFM). We present results of PFM studies done both on uniaxial relaxors Sr_1−xBa_xNb₂O₆ (SBN) and on cubic relaxors Pb[Mg_1/3Nb_2/3]_1−xTi_xO₃ (PMN-PT). Peculiarities of the polar structures below the transition temperature are analyzed. Quasi-static polar regions are revealed in a certain temperature range above T_C. In both cases the sizes of the observed clusters are much larger than expected for PNRs. The temperature dependence of the observed structures was investigated. The origin of these mesoscale polar regions, their relationship with the PNRs and their role in the phase transition are discussed.