Old and New Antiferroelectrics: Experimental Studies of Phase Transitions in Model Materials

Antiferroelectrics are a subcategory of ferroic materials that display no spontaneous polarisation
due to antiparallel ionic displacements. These materials undergo an electric field-induced transition
to a polar phase accompanied by the emergence of a spontaneous polarisation. As for ferroelectrics, heating up an antiferroelectric material above a certain temperature Tc will cause another phase transition towards a paraelectric phase.
Antiferroelectricity is currently the subject of a renewed interest, mostly due to a rising need
of new smart materials for applications such as energy storage, electrocaloric cooling or microelectronics. The most-studied antiferroelectric is lead zirconate PbZrO3perovskite. However, the understanding of its switching mechanism is still incomplete. In this work, we will first present our study on the sol-gel synthesis and characterisation of antiferroelectric polycrystalline thin films of canonical lead zirconate PbZrO3. We will notably highlight the realisation of an in-plane switching of our antiferroelectric samples grown on transparent substrates, as well as the optical observation of this switching through birefringence changes.
On a more fundamental side, the oldest and best-known model of antiferroelectricity was
defined by Kittel in 1951. No real unidimensional Kittel-like model material has, to our knowledge,
been identified yet. We will detail our spectroscopic study of the lattice dynamics of francisite
Cu3Bi(SeO3)2O2Cl which combines several inelastic scattering experiments. We will then discuss
how this study proves that francisite is, to our knowledge, the best candidate of a material displaying a displacive antiferroelectric phase transition.