R. Cach et al., DIELECTRIC-PROPERTIES OF BETAINE PHOSPHITE NEAR THE FERROELECTRIC PHASE-TRANSITION, Physica status solidi. a, Applied research, 148(2), 1995, pp. 585-595
The dielectric behaviour of a betaine phosphite [BPI: (CH3)(3)NCH2COO
. H3PO3] crystal is investigated around its ferroelectric phase transi
tion. The temperature dependence of the dielectric constant is measure
d for de bias fields up to 150 kV/m. The spontaneous polarization is m
easured using the Diamant-Drenck-Pepinsky circuit. The results are dis
cussed on a basis of the quasi-one-dimensional Ising model. The parame
ters obtained in this experiment have considerable anisotropy of inter
actions: J(parallel to)/k = 270 K, J(perpendicular to)/k = 21 K, and J
(parallel to)/J(perpendicular to) = 12.8. The model explains well the
temperature dependences of spontaneous polarization only in the temper
ature range 0 < (T-C - T) < 10 K. The field dependence of the maximum
dielectric constant epsilon(max) as well as the spontaneous polarizati
on close to T-C, can be described starting from the classical equation
of state. The equation coefficients are determined. However, the best
fit to the reciprocal permittivity data, in the paraelectric phase, i
s obtained for a second-order polynomial. In our opinion the macroscop
ic properties of BPI are considerably confused by the real structure o
f the crystals - defects, space charge, surface layers.