Domain Structure and Birefringence in Pyridinium Perchlorate and Pyridinium Fluoroborate Single Crystal

Abstract

Pyridinium perchlorate and pyridinium fluoroborate were grown and their successive phase transitions were studied by means of polarized microscopic observations and measurements of linear birefringence temperature changes. The microscopic observations revealed domain structure appearance at 245 K and 238.7 K for pyridinium perchlorate and pyridinium fluoroborate, respectively. This domain structure exists also in lower phases. Birefringence measurements confirmed two first-order phase transitions at 245.3 K and 231.5 K for pyridinium perchlorate and two continuous phase transitions at 238.7 K and 205.4 K for pyridinium fluoroborate.

Polarisation and Energy Barriers in Ferroelectric Pyridinium Perchlorate

“…More precise analysis of the total value of the spontaneous polarisation would be possible when the crystallographic structure of the ferroelectric phases II and III of the PyClO 4 crystal is determined. Hitherto, attempts of determination of the crystallographic structure of these phases have failed because the phase transition from the prototype R3m phase to the Cm phase is both ferroelastic and ferroelectric in character, which produces a complex ferroelastic domain structure in the crystal [11].…”

“…The value of spontaneous polarisation can be estimated knowing the dipolar moments of the molecules making the crystal and the probability of orientation of the dipoles along the ferroelectric axis [5][6][7]. The discovery of ferroelectric properties in certain pyridinium salts at the beginning of the 1990s aroused a new great interest in this group of compounds [8][9][10][11].…”

Dielectric nonlinear properties of pyridinium tetrafluoroborate single crystal near the ferroelectric phase transition

“…As predicted by Aizu [9] the phase transitions from I to II requires the appearance of domain structure of ferroelastic type. Polarized microscope observations [10] revealed domain structure with domain walls predicted by Sapriel [11]. PyBF 4 is probably a unique example of a multiaxial ferroelectric crystal undergoing a continuous phase transition [12].…”