The phase situation and ferroelectric properties in the mixed crystals [4-NH2PyH][SbCl4(1−x)Br4x]

The group of mixed crystals of general formula: [4-APyH][SbCl4(1−x) Br4x] with x ranging from 0 to 1 was studied by means of differential scanning calorimetry, dilatometry and dielectric spectroscopy. The ferroelectric properties are preserved for mixed crystals with replacement fraction, x, less than 0.30. Moreover, such a substitution of the chlorine atoms by the bromine ones significantly lowers the temperature of the structural phase transition shifting it from 240 K for pure [4-APyH][SbCl4] to about 185 K for the mixed crystals richer in bromine. The dielectric relaxation process exhibited by the mixed crystal with x = 0.90 in the radio-frequency region was analyzed and the activation energy was estimated (Ea = 18 kJ/mol). Additional measurements of single crystals X-ray diffraction and powder IR and Raman spectroscopy were performed. On the basis of the experimental results the phase diagram for mixed crystals has been proposed.