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The most characteristic functional property of antiferroelectric materials is the possibility to induce a phase transition from a nonpolar to a polar phase by an electric field. Here, we investigate the effect of this field-induced phase transition on the birefringence change of PbZr0.95Ti0.05O3. We use a transparent polycrystalline PbZr0.95Ti0.05O3 film grown on PbTiO3/HfO2/SiO2 with interdigitated electrodes to directly investigate changes in birefringence in a simple transmission geometry. In spite of the polycrystalline nature of the film and its moderate thickness, the field-induced transition produces a sizable effect observable under a polarized microscope. The film in its polar phase is found to behave like a homogeneous birefringent medium. The time evolution of this field-induced birefringence provides information about irreversibilities in the antiferroelectric switching process and its slow dynamics. The change in birefringence has two main contributions: One that responds briskly and a slower one that rises and saturates over a period of as long as 30 min. Possible origins for this long saturation and relaxation times are discussed.

Antiferroelectrics have been recently sparking interest due to their potential use in energy storage and electrocaloric cooling. Their main distinctive feature is antiferroelectric switching, i.e., the possibility to induce a phase transition to a polar phase by an electric field. Here, we investigate the switching behavior of the model antiferroelectric perovskite PbZrO3 using thin films processed by chemical solution deposition in different geometries and orientations. Both out-of-plane and in-plane switching configurations are investigated. The critical field is observed to be highly dependent on the direction of the electric field with respect to the film texture. We show that this behavior is qualitatively consistent with a phase transition to a rhombohedral polar phase. We finally estimate the importance of crystallite orientation and film texturation in the variations observed in the literature.

Antiferroelectric PbHfO3 is grown from atomic layer deposition precursors lead bis(dimethylaminomethylpropanolate) and tetrakis dimethylamino hafnium with H2O and O-3 oxidizers in thicknesses from 20 nm to 200 nm at a substrate temperature of 250 degrees C. X-ray analysis shows an as-grown crystalline PbO phase that diffuses into an amorphous HfO2 matrix upon annealing to form a randomly oriented, orthorhombic PbHfO3 thin film. Electrical characterization reveals characteristic double hysteresis loops with maximum polarizations of around 30 mu C/cm(2) and transition fields of 350 kV/cm-500 kV/cm depending on the thickness. Temperature-dependent permittivity and polarization testing show a phase transition at 185 degrees C, most probably to the paraelectric phase, but give no clear evidence for the intermediate phase known from bulk PbHfO3. The energy storage density for the films reaches 16 J/cm(3) at 2 MV/cm. A dielectric tunability of 221 is available within 1 V for the thinnest film. These results highlight the unique spectrum of properties available for thin film perovskite antiferroelectrics.

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.

Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase transition in francisite Cu3Bi(SeO3)(2)O2Cl at 115 K and show that it provides a rare archetype of a transition driven by a soft antipolar phonon mode. In the high-symmetry phase at high temperatures, the soft mode is found at (0,0,0.5) at the Brillouin zone boundary and is measured by inelastic x-ray scattering and thermal diffuse scattering. In the low-symmetry phase, this soft-mode is folded back onto the center of the Brillouin zone as a result of the doubling of the unit cell, and appears as a fully symmetric mode that can be tracked by Raman spectroscopy. On both sides of the transition, the mode energy squared follows a linear behavior over a large temperature range. First-principles calculations reveal that, surprisingly, the flat phonon band calculated for the high-symmetry phase seems incompatible with the displacive character found experimentally. We discuss this unusual behavior in the context of an ideal Kittel model of an antiferroelectric transition.