Practical applicability has nothing to do with the Debye (single relaxaton time) behavior. Most polymers in the solid state exhibit non-Debye relaxation (the Cole-Cole plot can be described by the so-called Havriliak-Negami function), inorganic glasses can be usually described by the Watts-Willams distribution, nevertheless they are useful from the practical viewpoint. Debye relaxation appears usually in liquids or in the case of point-defects of allmost perfect crystals. Real materials usually exhibit broad relaxation time distribution. The relaxation time can be usually characterized by the preexponential factor and by the activation energy. If only the preexponential factor exhibits distribution the case is simpler, the time-temperature superposition principle can be applied to the system (i.e. log tau can be shifted along the log frequency or log time axis with a temperature dependent shif factor). If the activation energy exhibits distribution, the material will be thermorheologically complex, the shape of the distribution function will vary with temperature. I suggest you to have a look at the following book if you have access to it: A.K. Jonscher: Dielectric Relaxation in Solids, Chelsea Dielectric Press Ldt., 1983, London.
According to Debye relaxation process: all dipoles in the system relax with the same relation time (which is called a single relaxation time approximation). This process usually found in rigid molecules.
@Fathi Sir and Ioannis Sir.......how Debye relaxation is related to some memory effect?
Is non-Debye relaxation behavior is a full-proof evidence that a dielectric material is liable to be used in the practical applications?
please give your comments.
Practical applicability has nothing to do with the Debye (single relaxaton time) behavior. Most polymers in the solid state exhibit non-Debye relaxation (the Cole-Cole plot can be described by the so-called Havriliak-Negami function), inorganic glasses can be usually described by the Watts-Willams distribution, nevertheless they are useful from the practical viewpoint. Debye relaxation appears usually in liquids or in the case of point-defects of allmost perfect crystals. Real materials usually exhibit broad relaxation time distribution. The relaxation time can be usually characterized by the preexponential factor and by the activation energy. If only the preexponential factor exhibits distribution the case is simpler, the time-temperature superposition principle can be applied to the system (i.e. log tau can be shifted along the log frequency or log time axis with a temperature dependent shif factor). If the activation energy exhibits distribution, the material will be thermorheologically complex, the shape of the distribution function will vary with temperature. I suggest you to have a look at the following book if you have access to it: A.K. Jonscher: Dielectric Relaxation in Solids, Chelsea Dielectric Press Ldt., 1983, London.
@Gyorgy Sir......I beg your pardon.....I studied in a research paper (please see the attachment) that Non-Debye relaxation behavior is expected to occur in all practical dielectric materials.
Yes, you are right. In that sense that pure Debye relaxation is very rare, therefore in almost all "practical" (i.e. real) materials you will fing non-Debye relaxation (which is a theoretical limiting case). I meand that "pracitcality" is not related to the Debye behavior using another sense of the word "practical": non-Debye materials are not more useful than Debye realaxors. I misunderstood your usage of the term.
prof. Dinesh kumar. If you understand the equivalent circuit phenonmena for Cole-cole plots, it is very much helpful to understand the Debye and non-Debye behaviour of solids. Here it is discussed only for the movement of ionic charges.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Material Characterization