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DF: Fachverband Dielektrische Festkörper

DF 3: Phase Transitions

DF 3.5: Vortrag

Montag, 25. Februar 2008, 12:00–12:20, EB 407

Novel complexity in the phase diagram of ferroelectrics — •Annette Bussmann-Holder¹, Helmut Büttner², and Alan R. Bishop³ — ¹Max-Planck-Institut Für Festköroerforschung, Heisenbergstr.1, D-70569 Stuttgart, Deutschland — ²Lehrstuhl für Theoretische Physik, Universität Bayreuth, Bayreuth, Deutschland — ³Los Alamos National Laboratory, Los Alamos, NM 87545, USA

The temperature/ doping dependent phase diagram of ferroelectric perovskite oxides is shown to be characterized by six different temperature scales: At high temperatures a crossover from paraelectric to paraelectric / ferroelastic behavior sets in followed by the onset of fluctuating ferroelastic clusters with doping and temperature dependent size. The cluster size anti correlates with their volume which defines another transition line. The onset of ferroelectricity is not sharp since para- and ferroelectric solutions coexist in a small temperature regime. The ferroelectric phase shows novel effects since from a certain transition temperature on this state is incomplete, i.e., ferroelastic clusters fluctuate in a polar matrix. Finally ferroelectricity is completely suppressed by quantum fluctuations. In addition, a novel phenomenon is discussed, where it is shown that the ferroelectric soft modes controls preceding structural instabilities