Polarizability space-charge

We can further describe the polarization, P, according to the different types of dipoles that either already exist or are induced in the dielectric material. The polarization of a dielectric material may be caused by four major types of polarization electronic polarization, ionic (atomic) polarization, orientation polarization, and space-charge (interfacial) polarization. Each type of polarization is shown schematically in Figure 6.24 and will be described in succession. In these descriptions, it will be useful to introduce a new term called the polarizability, a, which is simply a measure of the ability of a material to undergo the specific type of polarization. 

The final type of polarization is space-charge polarization, sometimes called interfacial polarization, and results from the accumulation of charge at structural interfaces in heterogeneous materials. Such polarization occurs when one of the phases has a much higher resistivity than the other, and it is found in a variety of ceramic materials, especially at elevated temperatures. The space-charge polarization, P c, has a corresponding space-charge polarizability, The two are related via a relationship of the form for the other types of polarization. 

The dielectric constant of a material is a measnre of its polarizability in response to an electric field. This polarizability is the resnlt of reorganization of charge, which can be in the form of interfacial or space charge motion, ionic motion, dipolar motion, and electronic motion (see Figure 3.2.3) [14]. The timescale of the charge redistributions determines the frequency dependence of this contribution to the dielectric constant for a given material. In the case of ionic motion, the frequency range is up to 10 Hz. 

The total capacitance in the walls of the pores is given by C, = c,L. This capacitance is attributed to double-layer effects, so it is usually a function of the potential. It can also be used to describe the space-charge polarization at the semiconductor-liquid junction if the spatial distribution of electrical charge as a function of potential is known. An ideally polarizable interface with charge transfer can be described by considering the charge transfer as a resistance, ret, which goes in parallel to the capacitance so that the impedance element yields an impedance such as ... 

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