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[en] In this paper, the effective pyroelectric coefficient and polarization offset of the compositionally step-like graded multilayer ferroelectric structures have been studied by use of the first-principles approach. It is exhibited that the dielectric gradient has a nontrivial influence on the effective pyroelectric coefficient, but has a little influence on the polarization offset; and the polarization gradient plays an important role in the abnormal hysteresis loop phenomenon of the compositionally step-like graded ferroelectric structures. Moreover, the origin of the polarization offset is explored, which can be attributed to the polarization gradient in the compositionally step-like graded structure.
[en] This review paper summarizes recent advances in the quickly developing field of nanoscale ferroelectrics, analyses its current status and considers potential future developments. The paper presents a brief survey of the fabrication methods of ferroelectric nanostructures and investigation of the size effects by means of scanning probe microscopy. One of the focuses of the review will be the study of kinetics of nanoscale ferroelectric switching in inhomogeneous electrical and elastic fields. Another emphasis will be made on tailoring the electrical and mechanical properties of ferroelectrics with a viewpoint of fabrication of nanoscale domain structures
[en] A MEMS electret vibration energy harvester with an embedded bistable electrostatic spring for broadband response is proposed. By using a vertical electret, the bistable potential can be realized without any complex structure or additional mechanism. Based on the 1D electrostatic model, a rigorous electromechanical model as well as an approximate model with reduced parameters are developed. Based on the normalized expression of the approximate model, which is identical to the velocity-damped resonant generator model, the performance of harvesters with the proposed mechanism has been characterized in detail for harmonic excitation, band-limited white noise, and colored noise. In addition, its performance has been compared with that of a conventional duffing-type bistable generator. It is confirmed that the present mechanism has advantages such as a lower frequency range, and outperforms the duffing counterpart for colored noise. (paper)
[en] Highlights: • This article summarizes the state-of-the-art research on progress of various fluoropolymer materials-based high performing TENGs. • We introduced an origin of the triboelectric effect and explained the working principle of TENGs with four different working modes. • Representative fluoropolymers and ferroelectric polymer, P(VDF-TrFE) based TENGs and their output performances are summarized. • The paper aims to cover materials for high performing TENGs and suggest future research direction in aspects; material, structure, circuitry. Triboelectric nanogenerators (TENGs), which have demonstrated that all moving things in the universe can generate electricity in a sustainable way are currently being developed to be integrated with electronics, and to improve user convenience. The electrically charged surface upon a contact electrification phenomenon caused by contact of the materials determines the output performance of TENGs. This review focuses on the electrification and surface charge density characteristics of various fluoropolymer-based materials as active materials that have been investigated to realize high performance TENGs, and the results of the study of their applications. Furthermore, the characteristics of electrification with differently polymerized P(VDF-TrFE) as TENGs’ active materials and their applications are reviewed. The boosted output performance characteristics when used as a matrix material and integrated with a composite system with a high dielectric constant material are also reviewed. Finally, the paper presents three perspectives on the direction of TENG research for future improvement, namely material, structure, and circuitry.
[en] The 10th International Conference on ferroelectricity was held on 3 - 7 September, 2001 in Madrid, Spain. At a plenary session of the conference, a talk was delivered, whose content is presented in the present paper. The paper is primarily concerned with the work of V L Ginzburg and other Russian physicists on the theory of ferroelectric phenomena. (conferences and symposia)
[en] We reveal that the role of the higher non-linear local interactions in the conventional theoretical models developed to describe phase transitions in type II incommensurate systems is underestimated. Their consistent consideration in the thermodynamic potential expansion allows one to remove key contradictions in explanation of the experimental data for ferroelectric Sn2P2Se6 in the vicinity of the modulated-commensurate phase transition point