Ferroelectrics

Ferroelectric perovskites are paraelectric (non-polar) above the Curie temperature, but become spontaneously polarized below it due to a loss of centrosymmetry.  The spontaneous polarization is often accompanied by a mechanical distorsion.  The anisotropy introduced by the polarization enables birefringences, and the loss of centrosymmetry enables piezoelectricity.  The soft modes of the phase transitions give rise to large dielectric constants, and the loss of symmetry enables domain switching between domains of symmetry-related polarizations.  All of these endow the material with fascinating properties that enable applications including optical modulators, non-volatile memories, capacitors, sensors, actuators and holographic storage media.
 

Our research on ferroelectrics has focussed on the following areas

Modeling of Semiconducting behavior

The range of phenomena, properties and applications of ferroelectrics have motivated a number of models of these materials going back to the pioneering work of Devonshire. Phase-field and other coarse-grained models which describe behavior at the domain and larger scales almost always assume that the ferroelectric is an insulator. However, a vast majority of the perovskite and polymer ferroelectrics are in fact wide-band-gap semiconductors.  Since ferroelectrics are often used with metal electrodes, we can expect the formation of depletion layers near the metal-ferroelectric interface, development of a built-in potential and associated band bending. This in turn has a significant impact on the ferroelectric properties and performance as observed by the dependence of the fatigue life and dielectric breakdown on the choice of electrodes. Further, it has been noticed that defects often decorate domain walls and that domain patterns can be manipulated using light via the generation of photoelectrons, highlighting the semiconducting nature of the ferroelectric. Therefore, we are interested in developing models for ferroelectrics which incorporate the semiconducing aspects.

Publications

  • Suryanarayana, P., Bhattacharya, K., 2012. Evolution of polarization and space charges in semiconducting ferroelectrics. Journal of Applied Physics 111, 034109. [LINK]