A TALK ON DIELECTRIC RELAXATION

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INTRODUCTION OF DIELECTRIC


A dielectric is an electrical insulator that can be polarized by an applied electric field.

When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization.

Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction.


DIELECTRIC RELAXATION


Dielectric relaxation is the momentary delay (or lag) in the dielectric constant of a material. This is usually caused by the delay in molecular polarization with respect to a changing electric field in a dielectric medium (e.g. inside capacitors or between two large conducting surfaces).


CONCLUSION


The dielectric behaviour of PMN appears strongly dependent both on temperature and on frequency.

Dielectric measurements performed in the 102-109 Hz and 150-400 K ranges allowed us to demonstrate two different relaxations: the first at high frequencies (HFR) which appears not only in the ferroelectric region but also in the paraelectric region, and the second at low frequencies (LFR) which is detected only below Tm.