Multi-scale characterisation of a ferroelectric polymer reveals the emergence of a morphological phase transition driven by temperature

Ferroelectric materials exhibit a phase transition to a paraelectric state driven by temperature - called the Curie transition. In conventional ferroelectrics, the Curie transition is caused by a change in crystal symmetry, while the material itself remains a continuous three-dimensional solid crystal. However, ferroelectric polymers behave differently. Polymeric materials are typically of semi-crystalline nature, meaning that they are an intermixture of crystalline and amorphous regions. Here, we demonstrate that the semi-crystalline morphology of the ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) strongly affects its Curie transition, as not only a change in crystal symmetry but also in morphology occurs. We demonstrate, by high-resolution nanomechanical measurements, that the semi-crystalline microstructure in the paraelectric state is formed by crystalline domains embedded into a softer amorphous phase. Using in situ X-ray diffraction measurements, we show that the local electromechanical response of the crystalline domains is counterbalanced by the amorphous phase, effectively masking its macroscopic effect. Our quantitative multi-scale characterisations unite the nano- and macroscopic material properties of the ferroelectric polymer P(VDF-TrFE) through its semi-crystalline nature.

Dielectric Properties of Modified Lead Zirconate Titanate

In this paper, the dielectric properties of modified i. e. alkali doped lead zirconate titanate Pb(Zr1- xTix)O3 has been studied. The composition Pb1-x (La1-zDz)x (Zry Ti1-y)1-x/4 O3;where x = 0.10, y = 0.70, z = 0.0, 0.1, 0.2, and 0.3, D= Na, K and Li has been prepared by conventional mixed oxide method at a temperature of 11000C. Dielectric constant and dielectric loss measurement of the sintered pellets has been measured. Dielectric measurement shows that the dielectric constant decreases with an increase in temperature. The results show that the dielectric loss is very small and decreases with frequency above 300°C. The increase in the dielectric constant observed at high temperatures and low frequencies is explained in the paraelectric state.

Quantum paraelectricity and induced ferroelectricity by germanium doping of (PbySn1–y)2P2S(Se)6 single crystals

In this paper we report a dielectric study on four single crystals Pb2P2S6, (Pb0.98Ge0.02)2P2S6, (Pb0.7Sn0.3)2P2S6 + 5% Ge and (Pb0.7Sn0.3)2P2Se6 + 5% Ge down to 20 K. A new quantum paraelectric state was reported in the Ge-doped samples at low temperatures. In all of these materials the non-classical T2 temperature dependences of inverse dielectric permittivity were observed. The dielectric constants of Pb2P2S6-based single crystals were measured between 20 and 300 K. The temperature dependences of dielectric permittivity were analysed on the basis of Barrett’s model as a signature of quantum paraelectricity.

Исследования электрофизических свойств сегнетоэлектрических пленок Ba-=SUB=-0.8-=/SUB=-Sr-=SUB=-0.2-=/SUB=-TiO-=SUB=-3-=/SUB=- в параэлектрическом состоянии

Phenomenological analytical expressions relating the ferroelectric film capacity to the coefficients of free energy decomposition in accordance to the degrees of substance polarization in paraelectric state are obtained. High-frequency capacitance-voltage characteristics of metal–Ba_0.8Sr_0.2TiO_3–metal structures have been measured at the temperatures above the transition point from ferroelectric phase to paraelectric one. The comparison of theoretical and experimental data has been resulted in plotting the dependences of Ba_0.8Sr_0.2TiO_3 film polarization on external voltage and determining the values of the parameters of the theory of phase transitions of second kind of Ginsburg–Landau for the objects under investigation.