Interfacial polarization, Physics

Interfacial polarization takes place whenever there is an storage of charge at an interface between two materials or between two regions in a material. As shown in the material has an equal number of positive ions and negative ions are assumed to be far more mobile. Under the presence of an applied field, these positive ions migrate to the negative electrode. The positive ions, however, cannot leave the dielectric and the crystal structure of the metal electrodes. They therefore simply pile up at the interface and give rise to a positive space charge in the bulk together constitute dipole moment that appear in the polarization vector p. The positive charge on the electrode, of course, appears as an increase in the dielectric constant. One of the typical examples of interfacial polarization is the grain boundaries that frequently lead interfacial polarization as they trap can charges migrating under the influence of an applied field. Dipoles between the trapped charges increase the polarization vector. Interfaces also arise in heterogeneous dielectric materials for example, when there is a dispersed phase within a continuous phase. The last three mechanisms are amenable to basic considerations and calculations, interfacial polarization, however, defines basic treatment. There is no general way to calculate the charges on neither interfaces nor their contribution to the total polarization of a material. Interface polarization is thus often removed from the discussion of dielectric properties. It would be completely wrong however to conclude that interface polarization is technically not significant because, on the one hand numerous dielectrics in real capacitors rely on interface polarization whereas, on the other hand, interface polarization if present may "kill" many electronic devices e.g. the MOS transistors. Normally interfacial polarization exists in the materials, however perfect, contain crystal defects, various mobile charge carries such as electrons (e.g.; from donor type impurities), holes or impurity ions or ionized host. H+ ion Li+ ion in ceramics and glasses are the general example of this type of polarization.

Posted Date: 7/7/2012 5:11:19 AM | Location : United States







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