Dresden 2003 – wissenschaftliches Programm
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DF: Dielektrische Festkörper
DF 7: Poster
DF 7.26: Poster
Mittwoch, 26. März 2003, 14:30–18:00, P2a
The Low-Temperature Phase of Chromium Doped Dimethylammonium Gallium Sulfate Hexahydrate (DMAGaS) Studied by Electron Paramagnetic Resonance — •Georg Völkel1, Rolf Böttcher1, Dieter Michel1, and Zbigniew Czapla2 — 1Universität Leipzig, Fakultät für Physik und Geowissenschaften, Linnéstrasse 5, D-04103 Leipzig, Germany — 2University of Wroclaw, Institute of Experimental Physics, Maxa Borna 9, PL-50204 Wroclaw, Poland
Dimethylammonium gallium sulfate hexahydrate (DMAGaS) and dimethylammonium aluminum sulfate hexahydrate (DMAAS) are isomorphous and ferroelastic at room temperature. Both they show an order-disorder type transition into a ferroelectric phase but only DMAGaS exhibits a further first-order transition into a low temperature non-ferroelectric phase. We report on electron paramagnetic resonance (EPR) measurements of chromium doped DMAGaS giving insight into the peculiar reorientation order of the polar dimethylammonium ions on a microscopic level. We found that the low-temperature phase of DMAGaS below 115 K shows a sequence of commensurate and incommensurate phases. Below 60 K the crystal becomes antiferroelectric. This unusual phase sequence can be well explained by means of a Landau approach using a great number of sublattice polarizations and more generally by the semimicroscopic extended DIFFOUR model.