Thermal and optical properties of the ferroelectric (C3N2H5)5Bi2Cl11 crystal |
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Authors: | Janusz Przes?awski Bogus?aw Kosturek Ryszard Jakubas |
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Affiliation: | a Institute of Experimental Physics, University of Wroc?aw, Max Born Sq.9, 50-204 Wroc?aw, Poland b Faculty of Chemistry, University of Wroc?aw, F. Joliot Curie 14, 50-383 Wroc?aw, Poland |
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Abstract: | Thermal (specific heat) and optical (linear birefringence) studies were performed for a new ferroelectric crystal (C3N2H5)5Bi2Cl11. Two phase transitions were confirmed and described. The first-order paraelastic-ferroelastic phase transition at 360 K was studied with a polarizing microscope. The continuous second-order phase transition at 165 K to the ferroelectric phase is described by the Landau model using specific heat and linear birefringence data. The Landau expansion coefficients B and C are of an order of magnitude higher than the closely related ferroelectric crystal; MAPCB — (CH3NH3)5Bi2Cl11. Thermal parameters (such as the excess enthalpy and the excess entropy ) of the continuous transition were estimated and discussed. The ‘two-site’ model describing the motion of three of the five imidazolium cations, which is proposed from the structural studies, is fully confirmed by the data from the ac-calorimetric measurements. |
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Keywords: | 64.70.Rh 65.40.Ba 78.20.Fm |
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