It is observed from the graph of dielectric loss vs log f, the value of dielectric loss is almost zero at higher frequencies. It was mentioned in the literature that the low value of dielectric loss suggests that the material is having less defect density and posses high optical quality. Can anyone suggest me the relationship between defect density and dielectric loss.
I think that the dielectric loss depends on the properties of your material without defect and the properties of defects (nature, %, distribution,...).
As an exemple you can find the publucations on "filled polymers". The filler can be considered as defects.
This answer could be wrong, but it is based on my conceptual understanding of dielectric loss. The relationship between defect density and dielectric loss depends on whether the defects in your sample material promote or diminish the movement of charges within the sample. In other words, do the defects increase or decrease charge mobility in your sample?
If the defects promote the movement of charge (increase mobility), the loss should be high; so in this case a high defect density would correspond to a high dielectric loss. But, if the defects in your sample degrade the movement of charges (decrease mobility) then the loss should be low; in which case a high defect density would correspond to a low dielectric loss.
Again, this answer may not be correct and I would love any feedback and discussion.
If a defect has an associated dipole moment that can change orientation, then it will contribute to the dielectric constant of the dielectric material. In general, at very low frequencies (high T) where all of a particular defect population can switch easily, dielectric constant is high and loss is low. As frequency increases (or T decreases) to the condition of resonance, the loss increases to a maxima and the real part of the dielectric constant to a minima. With further increases in frequency, this defect population is frozen out of any movement and both loss and dielectric constant decrease. Fig 27.7 of Ashcroft and Mermin's Solid State Physics (1976) is representative. (My5th edition of Kittel has the real part in Chap 13, fig 8, but does not plot the loss.) If you are looking for a good text to help you with understanding the frequency dependence of defects and identifying experimental methods, I would suggest Nowick and Berry's Anelastic Relaxation (1972).
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