What is the criteria for a material to have multiple relaxations?
First of all non-ideal or deviation from Debye behavior and origin of different relaxations can be due to Grain orientation, Grain boundary, Sub-grain boundary, Electrode effect and also be due to Interface functional groups. Usually multiple relaxations can be associated with polycrystalline structure too.
And in polymers as suggested by Gyorgy Banhegyi...!
Relaxations can be due to different chains present, related functional groups at interface and also due to electrode effect.
You can observe these multiple relaxation from Cole-Cole plot, but some times this plot can't give you sufficient information. Then you can try Modulus plane plot or comparison between imaginary parts of M'' and Z''.
I hope my answer will serve your purpose.
Further you can look at these research papers
1) http://apl.aip.org/resource/1/applab/v101/i2/p023114_s1?isAuthorized=no
2) http://apl.aip.org/resource/1/applab/v101/i25/p253104_s1?isAuthorized=no
Cheers!
You can get this information by Cole-Cole plot (use Impedance Spectroscopy). If the spectra follows Debye type nature than the system has single relaxation while its non-Debye nature confirm about multiple relaxation. According to Debye relaxation process all dipoles in the system relax with the same relation time (which is called a single relaxation time approximation). Debye relaxation appears usually in liquids or in the case of point-defects of almost perfect crystals. Pure Debye relaxation is very rare, therefore in almost all real materials you will find non-Debye relaxation.
To my knowledge, if we have a single depressed semicircle that represents the distribution of relaxations,the question remains....what is the origin for multiple relaxations in a material?
See chapter 6 in
http://novocontrol.de/pdf_s/APND3.PDF
http://dergiler.ankara.edu.tr/dergiler/55/1432/16094.pdf
http://crete.chem.cmu.edu/members/mary/mypapers/kurnikova_jcp96_105_00628.pdf
http://cdn.intechopen.com/pdfs/30966/InTech-Polymer_rheology_by_dielectric_spectroscopy.pdf
In liquids usually there is one central relaxation which exhibits distribution due to the cahnges in the local environment. The same is more or less tru to low molecular glasses. In polymers there can be relaxation phenomena widely decoupled from each other as e.g. main chain realxation (alpha) and side chain relaxation (beta) in e.g. polyacrylates. The degree of decoupling may depend on the temperature (they tend to merge at high temperature).
Dear Thirmal check if it is the answer of ur remaining quest:
A depressed semicircle typically represents a phenomenon with a distribution of relaxation times. This nonideal behavior could be correlated to several factors, such as grain orientation, grain boundary, stress-strain phenomena, and atomic defect distribution. A multitude of relaxation processes seems to coexist in real perovskite crystals or ceramics, which consist of a number of different energy barriers due to point defects appearing during the technological processes.
I agree with you,but what about in case of glasses,polymers where there are no grains and grain boundaries?
First of all non-ideal or deviation from Debye behavior and origin of different relaxations can be due to Grain orientation, Grain boundary, Sub-grain boundary, Electrode effect and also be due to Interface functional groups. Usually multiple relaxations can be associated with polycrystalline structure too.
And in polymers as suggested by Gyorgy Banhegyi...!
Relaxations can be due to different chains present, related functional groups at interface and also due to electrode effect.
You can observe these multiple relaxation from Cole-Cole plot, but some times this plot can't give you sufficient information. Then you can try Modulus plane plot or comparison between imaginary parts of M'' and Z''.
I hope my answer will serve your purpose.
Further you can look at these research papers
1) http://apl.aip.org/resource/1/applab/v101/i2/p023114_s1?isAuthorized=no
2) http://apl.aip.org/resource/1/applab/v101/i25/p253104_s1?isAuthorized=no
Cheers!
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