A reorientation of the PO₃-groups and radiation damage effect in ferroelectric phase transition studied by CW-EPR of PO₃²⁻radical in glycine·H₃PO₃single crystal

Apparent Shift of the Ferroelectric Ordering Temperature Observed by EPR in ?-Irradiated (Glycine) � H3PO4 Crystal

“…Glycinium phosphite (NH 3 CH 2 COO) Á (H 3 PO 4 ) undergoes the order±disorder transition to the ferroelectric state at T c = 224 K. The molecular mechanism of the phase transition is still not fully understood although a relatively large isotope shift of T c to 322 K after deuteration [1,2] suggests an important role of the hydrogen bonded protons, whereas the NMR data [3] show a complex molecular dynamics with coupled proton-glycine motions. Our EPR measurements of PO 2À 3 radicals have shown a coalescence of the EPR lines characteristic for ferroelectric phase transition at T* = 180 K [4]. In this note we show that T* is a local critical temperature, whereas the bulk ordering in the g-ray damaged crystal appears at T c .…”

Isostructural phase transition in m-carboxyphenylammonium monohydrogenphosphite

“…In GPI phosphite anions are hydrogen-bonded to infinite chains directed along the crystallographic c-axis (Averbuch-Pouchot, 1993a). The mechanism of the ferroelectric phase transition in GPI is connected to a dynamical disorder of the protons in the interphosphite hydrogen bonds, which is coupled to the motions of the ammonium groups of glycinium cations (Tritt-Goc et al, 1998;Morawski et al, 1998), whereas in BPI the phosphite anions are joined by hydrogen bonds in a dimer fashion into infinite chains along the ferroelectric b axis. Such an arrangement of protons in the hydrogen-bonded anions of the betainium phosphite crystal is related to the ferroelectricity observed in this compound (Fehst et al, 1993).…”

Dielectric Dispersion around the Ferroelectric Phase Transition in Partially Deuterated Glycine Phosphite

“…Since the phase transition temperature is shifted to 322 K by deuterium substitution for hydrogen [4,5], ordering of protons in hydrogen bonds expects to be important in the phase transition. The phase transition has been proved to have order-disorder nature from a critical slowing down of the dielectric dispersion of Debye type [4][5][6], hydrostatic pressure effect study [7], ultrasonic study [8][9][10], photopyroelectric study [11], Brillouin scattering [12,13], Raman scattering [4,14], and EPR study [15]. Recently, it is revealed by a series of neutron and X-ray diffraction experiments [16][17][18][19][20] that the hydrogen or deuteron in the bonds are disordered in the paraelectric phase and are ordered in the ferroelectric phase, respectively.…”