ABSTRACT

The relative permittivity r is a measure of how easily polarisation occurs in the presence of a field E. A high value of r means that the induced

polarisation from an applied field E is greater than that compared to a low value of r for the same value of E. In a ferroelectric material, such as BaTiO3, the ease with which domains can align depends upon the ease with which Ti4+ ions can overcome the energy barrier and jump to a new position within the crystal lattice. When one considers the probability of a jump to and from available energy minima the relative permittivity can

DkT

eP A

r>>1

, be shown to be expressed:

In the presence of an external field, the jump is more favourable in the direction of E. Domains in the direction of E tend

As T increases, the ions are more easily able to overcome the energy barrier and so, in the presence of an external field E, domains can grow more easily as the temperature is raised. This leads to an increase in polarisation P of the crystal with increasing T. That is, r increases with increasing temperature.