Why are gas and liquid isolators

Electrical properties of the insulators

Materials for electrical engineering pp 330-375 | Cite as


The electrical properties of semiconductors and metals, which we have dealt with in the two previous chapters, were mainly characterized by the fact that electrons exist in the material that can move almost freely. With the large group of substances called insulators (dielectrics), on the other hand, the valence electrons are so tightly and firmly bound to the atoms that electronic conductivity practically does not occur. The band structure of the insulators is very similar to the band structure of the semiconductors, only that the width of the forbidden zone is much larger in the case of the insulators. If one wants to draw a boundary line between the insulator and the semiconductor, one could define the boundary width of the forbidden zone as one hundred times the thermal energy at room temperature (300 K). This corresponds to a width of 2.6 eV. Substances with a forbidden zone smaller than 2.6 eV would be classified as semiconductors, substances with a larger width would be insulators. If one takes into account that the Fermi level lies roughly in the middle of the forbidden zone, then one can show in a short calculation that the Fermi function at the band edges has the vanishingly small value of 1.4 10−22 has, from which the number of free electrons per cubic meter of insulator is about 106 results. This is a value that is of the order of magnitude also true for good insulators. H. there is a single free electron in every cubic centimeter, and of course that is not enough to conduct electricity. In comparison, there are 10 in the intrinsic Si semiconductor16 and in metal 1023 Electrons per cubic centimeter. So if an electric field acts on the dielectric, then no electron flow can develop, but at most the charges in the atom will shift in opposite directions by a small distance in the field, and an atomic dipole is created because the charge centers no longer coincide . This process leads to polarization.

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  1. AZAROFF, BROPHY: Electronic Processes in Materials.Google Scholar
  2. CADY: Piezoelectricity.Google Scholar
  3. CONDON, ODISHAW: Handbook of Physics.Google Scholar
  4. HESS: The electrical breakdown in gases.Google Scholar
  5. HÜTTE: Taschenbuch der Materialkunde (Stoffhütte) .Google Scholar
  6. JAFFE, COOK, JAFFE: Piezoelectric Ceramics.Google Scholar
  7. KITTEL: Introduction to Solid State Physics.Google Scholar
  8. PASCOE: Properties of Materials for Electrical Engineers.Google Scholar
  9. ROST: Measurement of dielectric material properties.Google Scholar
  10. SACHSE: Ferroelectrics.Google Scholar
  11. SOLYMAR, WALSH: Lectures on the Electrical Properties of Materials. SONIN, STRUKOW: Introduction to ferroelectricity.Google Scholar
  12. VAN DER ZIEL: Solid State Physical Electronics.Google Scholar
  13. WANG: Solid-State Electronics.Google Scholar
  14. WERT, THOMSON: Physics of Solids.Google Scholar
  15. WIJN, DULLENKOPF: Materials in electrical engineering.Google Scholar

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© Springer-Verlag Vienna 1994

Authors and Affiliations

  1. 1. Institute for Materials in Electrical Engineering, Technical University of Vienna, Vienna, Austria