Ferroelectricity has been observed in various materials, including ceramics, polymers, molecular crystals, and hybrid organic-inorganic perovskites. These diverse materials offer exciting possibilities in the field of ferroelectric research. These properties are integrally related to the polar phase inherent in these materials, where the spontaneous arrangement of electric dipoles plays a key role in shaping their electronic structure and functional features. The polar phase introduces a rich diversity of phenomena, influencing the response of hybrid perovskites to external stimuli such as temperature variations and electric fields. Understanding the intricacies of this phase is crucial to realizing the full potential of these materials in various technological applications. Ferroelectric materials could potentially find applications in solar cells, where the polarization state can be manipulated to enhance photovoltaic efficiency. It is worth mentioning that ferroelectrics are a subgroup of pyro- and piezoelectrics, which find applications in the family of hybrid organic-inorganic perovskites as energy harvesters, infrared sensors, and environmental monitors. For this reason, researchers are actively investigating the factors influencing these properties of hybrid perovskites, including the crystal structure, composition, and the dynamic nature of the polar phase.
The subclass of hybrid organic-inorganic perovskites, which includes the methylhydrazine cation, has attracted significant attention due to its diverse range of exceptional properties. Particularly noteworthy is the ability of several of these perovskites to exhibit a polar phase and demonstrate remarkable ferroelectric and pyroelectric properties. Studies on related halides incorporating other organic cations, such as isopropylamine, have also confirmed the existence of the polar phase, making them intriguing candidates for pyro- and piezoelectric applications. The exploration and understanding of ferroelectricity in these materials continue to drive research and innovation in the field of functional materials and device engineering.

Thin-film ferroelectric composites, employing a poly(vinylidene fluoride-trifluoro ethylene) (PVDF-TrFE) matrix integrated with a unique blend of (1-x)SrFe₁₂O₁₉-(x)0.92(Bi₀.₅Na₀.₅TiO₃) – 0.08(BaTiO₃) (BNT-BT) particles, x=0.5, were prepared through spin coating technique on indium tin oxide (ITO) coated glass substrates. In the fabrication process, the PVDF-TrFE matrix is first dissolved in a suitable solvent. The ceramic particles are then integrated into the solution, ensuring uniform distribution and optimal particle interaction within the matrix, facilitating a smooth spin coating process. The resultant thin films are then subjected to a drying process at 140°C for 2 min to achieve the desired mechanical flexibility and structural integrity. The influence of varying concentrations of BNT-BT within the PVDF-TrFE matrix on the composite’s structural & micro-structural characteristics and functional properties was investigated. Comprehensive characterization techniques, including X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are employed to assess the microstructure and surface morphology of the films. Broadband impedance spectroscopy analyses showed improved interfacial polarization and an increased number of internal micro-capacitors as a relaxation source. The detailed exploration of the ce-ramic-polymer composite aims to shed light on the effects of particle size, shape, distributions, interfaces, and local crystalline structure/defects on the effective response of the macroscopic properties.
The anticipated outcome of this research is to unveil the potential of PVDF-TrFE-based composites in advanced applications, such as flexible sensors and actuators. The study contributes to the understanding of ceramic-polymer interactions and their impact on the overall performance.
The financial support from the Core Program of the National Institute of Materials Physics 2023 – 2026, Project PC2–PN23080202, funded by the Romanian Ministry of Research, Innovation and Digitalization is highly acknowledged.

Abstract: Last minute contribution – please contact the speaker for further details

PVDF and its co- and terpolymers are interesting materials due to their electrical and electroactive properties. Based on different structural properties, the polymers exhibit ferroelectric or relaxor-ferroelectric and, for example, piezoelectric or electrostrictive and electrocaloric properties. With different molecular weights, polar phases, crystallinities and crystallite sizes, these polymers are also excellent candidates for extensive investigation of structure-property relationships. In addition to studying the individual ferroelectric (e.g. P(VDF-TrFE) copolymers) and relaxor-ferroelectric polymers (e.g. P(VDF-TrFE-CFE) terpolymers) themselves, it is also possible to transform ferroelectric into relaxor-ferroelectric polymers, for example by means of various irradiation processes. Here, this transformation is demonstrated by structural modification on P(VDF-TrFE) copolymers by means of irradiation with electrons. First, we describe the preparation of P(VDF-TrFE) films as well as the performed irradiation processes, focusing on the usage of relatively low doses starting at 50 kGy up to high doses of 900 kGy. In detail, the transformation from ferroelectric to relaxor-ferroelectric properties is evaluated as a function of different irradiation doses. The accompanying transition from piezoelectric to electrostrictive, as well as the electrocaloric properties are also investigated. In order to evaluate the underlying modifications, the structural properties such as crystallinity and crystal sizes, polar phases, molecular masses, and cross-linking are analysed. Finally, the processes that take place simultaneously during irradiation, the reduction of the chain length and the cross-linking are described as a function of the irradiation dose. Based on these structural and electrical properties, the observed maximum electrocaloric activity of P(VDF-TrFE) copolymers irradiated with relatively low doses will be explained.