“…Depending on their symmetry and the size of anions, these compounds exhibit a large variety of interesting phenomena: phase transitions, ferroelectricity, dynamic orientational disorder of pyridinium cations, etc., [1][2][3][4]. The ferroelectric state was observed in pyridinium tetrafluoroborate PyHBF 4 (C 5 H 5 NHBF 4 ) [1], pyridinium perchlorate PyHClO 4 [2], pyridinium perrhenate PyHReO 4 [3], and pyridinium periodate PyHIO 4 [4]. Interest in studying the latter two compounds listed above is connected with the fact that their Curie temperatures are close to room temperature.…”