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7. (t0 points) (1) Identify the main polarization mechanism (choose one among four polarization origins) that can occur in the following materials. (a) Lead zirconium titanate (non-centrosymmetric structure like BaTio,): (b) Nitrogen (non-polar, covalent gas): (c) Hydrogen Fluoride (permanent dipoles): (d) Polycrystal composites (multi-grains) four polarization mechanisms, which one can respond to the highest (2) Among these frequency (e.g. >1015 Hz) of applied field? Why? nmTizing the electronic properties of materials.

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Lead zirconate titanate It has dipolar polarization. Lead zirconate titanate is an inorganic compound with the chemical formula Pb [ZrxTi1刈03 (OSxS1). Also called PZT, it is a ceramic perovskite material that shows a marked piezoelectric effect. PZT is also ferroelectric, which means it has a spontaneous electric polarization (electric dipole) that can be reversed in the presence of an electric field. Nitrogen A compound which has non-zero dipole moment is a polar molecule. Since, nitrogen gas has a triple bond between the two nitrogen atoms. Since there is no electronegativity difference between the two atoms and hence there is zero dipole moment of the bond. Hence, N2 is a non polar molecule Hydrogen fluoride In case of dipolar polarization, we have materials where the dipoles are present independent of each other, i.e. they dont interact and they can be rotated freely by an applied field unlike in case of ionic polarization. Due to the ability of molecules to move around randomly, liquids have very limited dipolar polarization contribution despite havinga permanent dipole moment for each molecule Polycrystalline composites It consists of Electronic Polarization. What it says is that the electronic polarization effect is generally very weak and contributes very little to the overall polarization. Haing said that, it must be borne in mind that some materials like Si which are covalently bonded and orbital do not have spherical symmetry and as a result the dielectric constants can be higher (for example Si has aboutEr 12) Polycrystalline composites. Electronic polarization loses its response in the ultraviolet region around 1015 Hz. In the frequency region above ultraviolet, permittivity approaches the constant ε0 in every substance, where ε0 is the permittivity of the free space. Because permittivity indicates the strength of the relation between an electric field and polarization, if a polarization process loses its response, permittivity decreases. As a result, atomic polarization is the fastest and typically persists at frequencies between 1013-1015 Hz. In contrast, ionic polarization is sluggish and typically occurs at frequencies between 102-1013 Hz while dipolar polarization involving movement of molecules happens below 10 Hz. Interface or space charge polarization occurs at frequencies below 10 Hz

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