Nonlinear dielectric constant and ferroelectric-to-paraelectric phase transition in copolymers of vinylidene fluoride and trifluoroethylene

Abstract

Second- and third-order dielectric constant ε2 and ε3 of three copolymers of vinylidene fluoride and trifluoroethylene were measured over a temperature range from 20 °C to higher than the ferroelectric-to-paraelectric phase transition temperature Tc . The thermodynamical theory predicts that ε2 is negative below Tc and vanishes at Tc , whereas, for the second-order transition, ε3 is positive below Tc but turns to negative at Tc and, for the first-order transition, ε3 does not change its sign below and above Tc . According to this criterion, it is concluded that the transition is of the second order for a copolymer with vinylidene fluoride fraction of 52 mole %, but of the first order for 65 and 73 mole % copolymers. This conclusion can explain the difference in slope of ε2 versus remanent polarization among the copolymers.

Non-Linear Dielectric Response of Ferroelectrics, Relaxors and Dipolar Glasses

“…A similar calculation for a discontinuous PTs, where B < 0 and C > 0, yields χ 3 > 0 at all temperatures, in particular also above PT (Ikeda et al, 1987). Fortunately from an www.intechopen.com experimental point of view χ 3 is given by this same equation (8) within paraelectric phase independent of the ferroelectric PT order.…”

“…After successive differentiation of this equation with respect to P one obtains the following susceptibilities (Ikeda et al, 1987): (…”

Исследование фазовых переходов сегнетоэлектрика SС(NH-=SUB=-2-=/SUB=-)-=SUB=-2-=/SUB=- в нанопористых матрицах на основе Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

“…Анализ нелинейных диэлектрических свойств в се-гнетоэлектриках был сделан в работе [18] с помощью теории Ландау-Гинзбурга для фазовых переходов пер-вого и второго рода. Сегнетоэлектрический переход при температуре T c в тиомочевине является переходом первого рода.…”

“…Сегнетоэлектрический переход при температуре T c в тиомочевине является переходом первого рода. В этом случае диэлектрическая прони-цаемость третьего порядка ε 3 определяется следующим соотношением [18]:…”

A method for measuring the nonlinear response in dielectric spectroscopy through third harmonics detection

“…Understanding nonlinear effects allowed decisive breakthrough in condensed matter physics. Spin glasses [1,2,3,4,5,6], ferroelectric, freezing, or dipolar glass transitions [7,8,9,10,11,12,13,14,15,16,17,18,19], isotropic-liquid crystal transition [20,21] or binary mixtures [22,23], superconductivity [24,25,26,27,28,29], field [30,31,32,33,34] or heating [35,36,37,38,39,40] effects in electrical transport, heating due to electric field excitation of supercooled liquids [41,42] are a few among many topics where non linear measurements have proven to be a precious tool.…”