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Relaxation times/frequencies of Polarization Mechanisms

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citw
#1
Oct16-13, 03:47 AM
P: 72
Why do polarization mechanisms decrease with frequency in the following order:

Space charge/Interface

Dipole

Ionic

Electronic

See page 3 in the attached document for reference.

Edit: corrected error in wording
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File Type: pdf F. DIELECTRIC BEHAVIOR.pdf (78.8 KB, 1 views)
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DrDu
#2
Oct16-13, 03:59 AM
Sci Advisor
P: 3,593
I would rather say they decrease in that order!
In general the maximal frequency depends on the inertia of the degrees of freedom. It is clear that an ion can't move as fast as an electron as it is heavier.
A more elaborate argument goes like this: The degrees of freedom have characteristic frequencies at which absorption takes place. For ordinary conduction/ space charges this frequency is zero (Drude), for dipole orientation there is a range of frequencies up to the microwave and finally ionic and electronic transitions occur in the IR and UV part of the spectrum.
Now the real part of the dielectric constant can be obtained from this absorptive part by a Kramers Kronig transformation.
citw
#3
Oct16-13, 04:06 AM
P: 72
Quote Quote by DrDu View Post
I would rather say they decrease in that order!
In general the maximal frequency depends on the inertia of the degrees of freedom. It is clear that an ion can't move as fast as an electron as it is heavier.
A more elaborate argument goes like this: The degrees of freedom have characteristic frequencies at which absorption takes place. For ordinary conduction/ space charges this frequency is zero (Drude), for dipole orientation there is a range of frequencies up to the microwave and finally ionic and electronic transitions occur in the IR and UV part of the spectrum.
Now the real part of the dielectric constant can be obtained from this absorptive part by a Kramers Kronig transformation.
The lower frequency of interface and dipole polarization, in that order, relative to ionic polarization is what I'm having trouble with. I'm not sure why interfacial polarization occurs at the lowest frequency or why dipole/orientation polarization occurs at a higher frequency than interfacial, but a lower frequency than ionic.

DrDu
#4
Oct16-13, 05:50 AM
Sci Advisor
P: 3,593
Relaxation times/frequencies of Polarization Mechanisms

Interface polarization is due largely to classical currents of charge which are described by the Drude formula, i.e. a resonance at zero frequency. Dipole orientation is rotational motion of the dipoles which has resonance poles in the microwave/ far IR. "Ionic" polarization refers to the polarization due to optical phonons whose resonance frequency is in the IR.
citw
#5
Oct16-13, 08:19 AM
P: 72
Quote Quote by DrDu View Post
Interface polarization is due largely to classical currents of charge which are described by the Drude formula, i.e. a resonance at zero frequency. Dipole orientation is rotational motion of the dipoles which has resonance poles in the microwave/ far IR. "Ionic" polarization refers to the polarization due to optical phonons whose resonance frequency is in the IR.
Ok, I think I can figure out the dipole/ionic polarization from here, but I haven't seen anything relating Drude to interface polarization. Do you have any references describing this?
DrDu
#6
Oct17-13, 01:54 AM
Sci Advisor
P: 3,593
No, I have no reference. But as far as I understand, boundary polarization is an effect describable using ordinary macroscopic electrodynamics. So you can write down some equivalent RC networks etc whose characteristic frequencies are very low compared to the other effects mentioned.
Also the characteristic frequency of the conductivity which determines the R is 0, at least in Drude theory.


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