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RESEARCH PRODUCT

DSC, Dilatometric, Dielectric, and1H NMR Studies of Phase Transitions and Molecular Motions in [N(C2H5)4]3M2Cl9 (M = Sb, Bi) Crystals

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Results in the dependence of stoichiometry of obtained tetraethylammonium (TEA) chloroantiomonate and chlorobismuthate salts on the molar ratio of reactants used in the synthesis are presented. Seven tetraethylammonium salts are obtained: (TEA) 6 M 8 Cl 30 , TEAMCI 4 , (TEA) 3 M 2 Cl 9 (M = Sb, Bi) and (TEA) 2 SbCl 5 . Preliminary X-ray diffraction studies on (TEA) 3 M 2 Cl 9 (M = Sb, Bi) show that they are isomorphous, crystallizing at room temperature in monoclinic symmetry. The dilatometric, dielectric, and DSC studies show that (TEA) 3 Bi 2 Cl 9 undergoes two phase transitions at T c2 = 144 K and at T c1 = 322 K while (TEA) 3 Sb 2 Cl 9 undergoes three transitions at T c3 = 185, T c2 = 219, and T c1 = 321K. Both crystals are ferroelastic below the ferro-paraelastic transition at T c1 . The room temperature domain structure belongs to the Aizu species 6/mmmF2/m. The spin lattice relaxation times and the values of the second moments of the 1 H NMR line for the (TEA) 3 Sb 2 Cl 9 crystal are measured in the temperature range of 50 to 350K. Three minima of T 1 are observed. Two low-temperature minima are attributed to CH 3 group reorientations, while the high-temperature one to reorientations of the whole cations. The activation energies for the processes are determined.