After curie temperature dielectric constant comes down. but in some materials it starts increasing again for high temperature and low frequencies. i want to know...why this happens? and how to prove or establish its reasoning?
Hello Sonu, you explained something which is an understanding of plot between dielectric constant and frequency. this i can understand very well. Now let us consider the frequency is fixed (take 100Hz).
in case of any ferroelectric material after curie temperature dielectric constant starts decreasing but in case of low frequencies it starts increasing again after a decrease while this doesnot happen on high frequency. i want to know its reason.
In the low frequency regime it may be important (depending on the conductivity of the material under investigation) to consider interfacial polarization effects which originate from:
i) the presence of electrons trapped with a finite lifetime in localized states near the interface
ii) space charge polarization effects due to the presence of mobile ions in the material which are virtually always present, and
iii) blocking layer with different density of charge carriers owing to band bending near the electrode-dielectric interfaces, causing charge injection from the electrode into the dielectric or vice versa charge depletion due to different work functions of electrode and the dielectric material.
At low frequencies the total impedance is predominately governed by the interface resistance (due to item i)-iii)). This resitstance shows a semicontuctor temperature characteristics (Arrhenius behaviour). Therefore, after passing TC the permittivity will start to increase again with increasing temperature at low fixed frequencies. As it is evident, for very low conductive materials, interfacial polarization effects only arises at very low frequencies.
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