Ferroelectric properties of pyridinium perrhenate

Abstract

Polycrystalline pyridinium perrhenate has been studied over a wide range of temperatures by differential thermal analysis, differential scanning calorimetry, proton NMR spectra and relaxation, and dielectric permittivity measurements. Two solid-solid phase transitions at 250 and 333 K have been revealed and the pyridinium cation reorientations characterized. The higher transition appears to be the Curie point of a new ferroelectric compound.

Critical Slowing Down in Ferroelectric Pyridinium Tetrafluoroborate

“…The single crystals were rhombohedrons of the maximum size 15 Â 15 Â 15 mm 3 . The sample to be studied was cut out of this single crystal in the shape of a rectangular prism of the size 3 Â 3 Â 0X5 mm 3 . Dielectric measurements were performed along the ferroelectric direction, i.e.…”

“…Recently discovered ferroelectric properties of pyridinium tetrafluoroborate C 5 H 6 N BF À 4 abbreviated as PyBF 4 [1] were also detected in other pyridinium salts [2,3]. A characteristic feature of this new ferroelectric family is the occurrence of a sequence of two-phase transitions; in PyBF 4 there are the ferroelectric phase transition at T 1 238X7 K and another transition at T 2 204 K. Earlier NMR studies of pyridinium salts [4 to 7] proved the occurrence of reorientation of both pyridinium cation and BF 4 anion in the symmetric high-temperature phases.…”

Structural phase transitions in pyridinium perrhenate at high pressure

“…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.…”

The structure and dielectric properties of ionic compounds with flexible ammonium moiety

“…The most important step for discovering the high temperature or room temperature molecule-based ferroelectrics is designing or searching for the high temperature phase transition compounds [12][13][14][15]. Moreover, the introduction of molecular motions to solid state material is one of the effective methods to construct the orderdisorder type phase transition compounds [16][17][18][19][20][21]. Generally, plastic crystalline states such as hexamethylethane, cyclohexane, adamantane, and fullerene (C60), whose structures are flexible, have a tendency to lead to the phase transition triggered by temperature [22][23][24][25].…”