The Dielectric Response of Electro-active Dielectrics: Charge-spring Model for U

主讲人 : Reimund Gerhard（德国波茨坦大学、教授、美国物理学会院士和欧洲物理学会院士）

Mass-spring or bead-spring models such as the Rouse model are used in the theory of macromolecular materials. Charge-spring models help to understand the interaction between the electrical and the mechanical domains in materials at atomic, molecular, crystalline and even macroscopic length scales, but have played a smaller role. The best-known charge-spring model is the Lorentz oscillator introduced by Hendrik A. Lorentz for treating the frequency spectrum and the resonance behaviour of atoms by assuming that electron and nucleus are coupled by a spring-like force. With the Lorentz oscillator model, the high-frequency resonance behaviour of dielectrics in the THz to PHz range can be easily explained.

In contrast, it is usually assumed that the dielectric function of materials at lower frequencies only exhibits relaxation behaviour, but no resonance phenomena. Dielectrics with quasi-permanent dipole polarisation and/or charges, however, show electro-mechanical resonances at frequencies in the kHz to GHz range - depending on the length scale of the relevant mechanical oscillator(s). The experimental technique of dielectric resonance spectroscopy for the investigation of piezoelectric materials was developed from these observations. Such resonances may also be illustrated and modelled with charge-spring arrangements.

The charge-spring model will be summarised together with recent refinements that take the limited size of the relevant springs between the two charges or charge  s of opposite polarity into account. It will be shown that the corrections lead to reasonably good predictions of the observed piezoelectric thickness coefficients if the spring behaviour (i.e. the relevant elastic-modulus tensor component) and the amount of charges at the ends of the springs (i.e. the effective dipole polarisation) are known for a piezoelectric or electromechanical material. The model does not only help to understand and predict piezoelectricity in dielectrics more easily, but it is also a very good tool for teaching the fundamentals of electroactive materials.

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主讲人简介：

Member of American Physical Society (APS, Fellow), European Physical Society (EPS), German Physical Society (DPG), Institute of Physics (IoP), Institute of Electrical and Electronics Engineers (IEEE, Fellow), Acoustical Society of America (ASA), Materials Research Society (MRS), Information Technology Society (ITG), and Berlin-Brandenburg Society of Polymer Research (BVP) More than 300 scientific and technical publications in professional journals, conference proceedings, and books (not including published abstracts) Grants from European Union (EU), Deutsche Forschungsgemeinschaft (DFG), German Academic Exchange Service (DAAD), Federal Ministries of Education and Research (BMFT/BMBF) and of Economics and Technology (BMWi), Brandenburg State Ministry of Science, Research and Culture (MWFK), several foundations and industrial companies such as Arkema, Bayer MaterialScience (BMS), Tarkett, etc.