What does relaxation time or rearrangement time in dielectrics actually stand for? If Quartz has a relaxation time of 51 days, does it mean quartz takes 51 days for charges inside it to rearrange with an applied electric field? Then how can it act as a dielectric?
it means how long it takes to become neutralized. relaxation time is small in metals and large in semiconductors and insulators.
Dear Mr. Dinesh,
we have many relaxation times in dielectrics. For some polarisation effects ( electronic , ionic , .. ) we have relaxation processes. This relaxation effects are important for the loss effects.
And we can measure this effects with the cole cole plot.
Sincerely yours
F. Gräbner
I still don't get it. If it takes a long time for dielectrics to return to equilibrium, won't it take the same amount of time to get disturbed with an applied electric field?
I see that relaxation time has two definitions:
1. The delay in response to an applied electric field, and
2. Time taken by atoms to return to equilibrium with the withdrawal of applied field.
If relaxation time for dielectrics is huge, then won't the atoms take a long time to orient and reorient?
Then how does a material act as a dielectric?
Does relaxation time depend on the intensity of the applied electric field?
In my simple understanding, dielectric relaxation time is the time scale of the relaxation of mobile charge carriers in materials. It's not about the bound charges, the charges in dipole. Suppose that you have a dielectric material but with some electronic conductivity. If you make a capacitor using this dielectric and store a charge Q, the capacitor gets discharged over time because of its own conductivity. If you do some analysis, the charge on the plates of the capacitor decays exponentially with time with a relation Q = Q(0) exp(-t/\rho\epsilon) where \rho and \epsilon are the resistivity and permitivity of the material respectively. The decay time (\rho\epsilon) is called dielectric relaxation time.
In Quartz, the dielectric relaxation time is very long because of its very high resistivity (very low carrier concentration). However it does not mean you can not use it as dielectric material, because when you make capacitor, the free charge carrier polarization is not used. Dipole, ionic, electronic polarization are the sources of capacitance not the free carrier polarization. Free carrier polarization discharges the capacitor, an unwanted effect.
Do we need to have high relaxation constant or low relaxation constant value to be used in Pyroelectric detectors?
if the increase in the value of polarization suddenly decrease with increase in frequency, at that point the system is in dielectric relaxation. ..
it is the time scale of relaxation for moving of charge carriers in materials.
The process of relaxation is a process that helps a system to acquire the equilibrium state in which the system is most relaxed. Depending on the magnitude of disturbance imposed different molecular entities respond differently some respond quickly and some slowly for example electronic polarization is very rapid followed by ionic polarization. Orientation polarization is slower than ionic polarization. Space charge polarization is very slow. When P is the maximum polarization attained by the dielectric, tr is the relaxation time for a particular polarization process, the dielectric polarization process can be expressed as P(t) = P[1-exp(-t/tr )]. The relaxation time varies for different polarization processes. Dr. B R Gupta, [email protected]
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