Böhmer, RolandLunkenheimer, P.Vij, J. K.Svare, I.2008-06-132008-06-131990-06-18Böhmer, R.; Lunkenheimer, P.; Vij, J. K.; Svare, I.: Correlated reorientations in NH4Al(SO4) · 12 H2O single crystals. In: Journal of Physics: Condensed Matter Nr. 24, Jg. 2(1990), S. 5433-5438, doi: 10.1088/0953-8984/2/24/014.http://hdl.handle.net/2003/2556110.17877/DE290R-7496Single crystals of aluminium ammonium alum NH4Al(SO4)2.12H2O were investigated using dielectric spectroscopy in the frequency range 1 kHz to 1 GHz. On approaching the ferroelectric transition at 58 K from above, a monodispersive polar mode is observed to slow down. The relaxation data can be described in terms of a pure Arrhenius law. The analysis of the dielectric loss reveals that in the paraelectric phase the static susceptibility cannot be described by a single Curie-Weiss law. The thermal variations of the Curie constant indicate that the dipolar correlations of the ammonium ions increase as the temperature is lowered.enIOP Publishing53010.1088/0953-8984/2/24/014article (journal)