Ferroelectricity in Gly · H3PO3 crystal

Ultrasonic Studies of Ferroelectric Phase Transition in Gly-H3PO3 Crystals

“…Two kinds of symmetrical hydrogen bonds with a double potential well for protons exist in this crystal, and ordering of protons could be expected below room temperature. DSC and dielectric measurements [2] have revealed a ferroelectric phase transition at T c = 225 K. Although the proton ordering is expected along the c-axis, the dielectric investigations showed the appearance of spontaneous polarization below T c along the 6-axis with the Curie-Weiss type anomaly of the corresponding dielectric permittivity in the vicinity of this phase transition. In this sense, GPI differs from betaine phosphite (BPI) in which the ferroelectricity is connected with ordering of protons along ferroelectric axis [3].…”

Proton Ordering Model of Phase Transitions in Hydrogen Bonded Ferrielectric Type Systems: The Gpi Crystal

“…The absolute value of P s in the state of saturation (∼ 5 × 10 −3 C/m 2 [7]) is considerably smaller in comparison to other crystals of hydrogen bonded fam-ily. A large anomaly of permittivity in the c-direction has also been detected; at room temperature ε c is higher than ε b [7]. Apart from the structure investigations, the measurements of frequency dependence of dielectric constant also lead to the conclusion that the phase transition in GPI is of the order-disorder type [8,9].…”

“…We see that due to the considered mechanism the χ zz component of susceptibility can about three times exceed the χ yy component. The observed ratio of the ε c and ε b permittivities at room temperature is much larger (ε c /ε b ∼ 10 [6,7]). The long-range interaction, which favours the proton arrangement characteristic of the hypothetic F phase, can be the additional reason for such an anomaly.…”

“…The temperature behavior of the ε b component as well as the spontaneous polarization P s were studied; the conclusion was made that the phase transition can be regarded as the one close to a tricritical [6]. The absolute value of P s in the state of saturation (∼ 5 × 10 −3 C/m 2 [7]) is considerably smaller in comparison to other crystals of hydrogen bonded fam-ily. A large anomaly of permittivity in the c-direction has also been detected; at room temperature ε c is higher than ε b [7].…”

“…The long-range interaction has been modelled by two parameters Φ andΦ responsible for the interaction along a separate chain and between chains, respectively: [7]) and saturated spontaneous polarization (P s = 5 × 10 −3 C/m 2 [7]). In this case, for susceptibility we haveχ zz = 25−35 (figure 3b) at T > T c , which corresponds to the change of the true susceptibility from 7 to 10 (the coefficient µ 2 0 /ε 0 v c (j + j ) is equal to 0.28 at the chosen parameter values).…”