Dielectric relaxation of space charges and polarons in ferroelectric perovskites

Abstract

In all ferroelectric perovskites, intentionally introduced or “unwanted” point defects do play a role in the dielectric spectra and in the conductivity. Above room temperature, space charge relaxation at the electrodes interfaces are observed. This can be of interest in the context of the nowadays applications of ferroelectric thin films.

At liquid helium temperatures much more localised dielectric relaxation occurs. Special emphasis will be brought on SrTiO₃ which has received renewed interest at the beginning of the nineties and for which a wealth of reliable experimental data are available. Considering that a gradual freezing of polarized objects is occurring at low temperatures, one can reconcile most of these data within the same model. Even more interesting, one can show that point defects and quantum fluctuations do contribute to this freezing. This lead us to the new concept of quantum polarons which are very specific to SrTiO₃.

Key Words:

• dielectric relaxation
• space charges
• polarons
• perovskites