3D Electron Diffraction on Ferroelectric Perovskites

Session

Poster Session One

Authors

Dr. Andrea Griesi (2), Dr.ssa Valentina Vit (3), Dr.ssa Arianna Lanza (2), Dr. Fabio Orlandi (1), Prof.ssa Lara Righi (4), Dr. Mauro Gemmi (2)

Affiliations

1. ISIS Facility
2. Istituto Italiano di Tecnologia
3. UniPr
4. Unipr

Keywords

doubly ordered perovskite 3D electron diffraction modulated structure crystallography

Abstract text

The doubly ordered pervoskites AA’BB’O6 have been known since 1984, but detailed structural studies have only been carried out in recent years. Perovskites have structural and compositional flexibility, which allow us to alter the conduction bandwidth and strength of the magnetic super-exchange interactions. As such they provide a mechanism for fine tuning the electrical, magnetic and optical properties[1].

The crystal structures of several doubly ordered AA’BB’O6 perovskites have proven to be more complex than originally thought. Previous studies report complexity of the structure, such as compositional and/or positional modulations and twinnig of the octahedral tilt system.

NaLaCoWO6, a promising ferroelectric material, is one example of this structural complexity, showing a monoclinic average structure and a still unexplained temperature-dependent modulation[2].
 Moreover, NaLaCoWO6 can only be obtained in nanocrystalline form, thus making single-crystal XRD methods not applicable and powder methods extremely difficult. In such cases, 3D precession electron diffraction is the method of choice as it makes it possible to collect 3D diffraction data from single nanocrystals. This allows us to observe and resolve the modulation and reveal investigate local features of the structure[3].

Tiny changes of the crystal structures determine alterations of electric properties and could represent the key to understand the chemical mechanism governing the electric field-induced transitions. From our studies on NaLaCoWO6 with 3D PED at variable temperature, we could determine the modulation vector and superspace symmetry. Combining PED data with NPD and XRPD, we solved the (3+1)D modulated structure. An additional challenge is to use electron diffraction to reveal the structural changes induced by the application the of an electric field on NaLaCoWO6

References

1 – G. King, J. Mater - Chem 2010, 20, 5785-5796;
2 – P. Zou, C. Darie et al. - Inorg. Chem. 2019, 58, 81−92;
3 – A. Lanza, M. Gemmi et al. - Acta Cryst. (2019). B75, 711-716.