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DF: Dielektrische Festkörper

DF 7: Poster

DF 7.24: Poster

Mittwoch, 26. März 2003, 14:30–18:00, P2a

Dielectric properties of a DMAGaS/DMAAS mixed crystal — •Juras Banys¹, Georg Voelkel², R Boettcher², D Michel², and Z Czapla³ — ¹Faculty of Physics, Vilnius University, Sauletekio 9, 2040 Vilnius, Lithuania — ²Faculty of Physics and Earth Sciences, University of Leipzig, Linnestrasse 5, D-04103 Leipzig, Germany — ³Institute of Experimental Physics, University of Wroclaw, Maxa Borna 9, PL-50204 Wroclaw, Poland

Dimethylammonium gallium sulfate hexahydrate (DMAGaS) and dimethylammonium aluminum sulfate hexahydrate (DMAAS) crystals are ferroelastic and exhibit an order - disorder type phase transition into a ferroelectric phase at 152 K and 134 respectively. DMAGaS shows further phase transition into a low temperature phase at 116 K. EPR investigations of DMAGaS showed the existence of modulated phases at low temperatures. The behaviour of phase transitions in pure DMAAS and DMAGaS crystals have been already investigated in detail. In this contribution the results of the dielectric measurements of the mixed crystal (DMAGaS)₀.9(DMAAS)₀.1 are presented. The phase transition temperatures have been observed at 137 and 104 K. Debye type dielectric dispersion have been observed above the first phase transition. In the intermediate ferroelectric phase dielectric dispersion has been described with Cole - Cole formula due to the distribution of the relaxation times. In the intermediate phase two relaxational processes have been observed. At the first phase transition the soft mode softens up to 411 kHz. The activation energy of the soft mode in the paraelectric phase has been obtained.