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Séminaire Magnétisme frustré

Jeudi 11 Juin à 14h00,
Salle Rémy Lemaire, k223,

Orateur : Sébastien Saitzek (UCCS, Univ Artois)
"Microstructural studies and piezoelectric properties of Ln2B2O7 thin films (Ln=Lanthanide ; B=Ti or Zr) with a layered perovskite or a frustrated pyrochlore-type structures"

Abstract

The Ln2B2O7 oxides (Ln = lanthanide and B = Ti or Zr) have a high attractiveness in the scientific community because of their strong multifunctional potential. This family of compounds has catalytic, optical and piezo-/ferro-electric properties. For example, they are used for the degradation of VOCs pollutant by photo-catalysis. In optics, they can be used as an insertion matrix for rare earth and enable the development of new phosphors. In their monoclinic structure, these materials also exhibit piezo-/ferro-electric and pyro-electric properties with a high Curie temperature (Tc∼1500 ° C). This feature enables to consider use in extreme environments, such as achieving systems Micro- / Nano-electromechanical (M/NEMS) or piezo injectors for automotive or aerospace industry (operating at high temperatures). More recently, it has also been shown that this family could also have a multiferroic character at room temperature when the B site is partially substituted by a transition element such as Co, Fe, Mn, Cr [1].

In this work, we will present the synthesis of Ln2Ti2O7 thin films by the Pulsed Laser Deposition (PLD) technique or the sol-gel method by focusing on the structural stability limit of layered-perovskite structure (with respect to the pyrochlore structure) depending on the nature of substrate and of the ionic radius [2]. We will show the ability to synthesize new Ln2Ti2O7 phases metastable (Ln = Sm, Gd, Eu) presenting ferroelectric properties when deposited on low lattice mismatch substrates compared to the structure of layered-perovskites. The results of structural characterization made by X-ray Diffraction High-Resolution (in reciprocal space maps, pole figures or φ-scan) and Transmission Electron Microscopy will be presented and discussed in order to establish epitaxial relationships. The ferroelectric properties will also be shown through studies conducted at the nanoscale by Piezoelectric Force Microscopy (PFM). In the last part, we will present a study on the ferroelectric properties of La2Zr2O7 thin films deposited on (110)-oriented SrTiO3 substrate, having a pyrochlore-type frustrated structure [3]. Finally, we will discuss the multiferroic properties of these compounds through the recent studies in the literature.

[1] G. Gong, Y. Qui, G. Zerihun, Y. Fang, C. Yin, C. Zhu, S. Huang, S. Yuan, Multiferroic properties in transition metals doped La2Ti2O7 ceramics, Journal of Alloys and Compounds, 2014, 611, 30–33.
[2] Z. Shao, S. Saitzek, P. Roussel, R. Desfeux, J. Mater. Chem., 2012, 22 (47), 24894 – 24901.
[3] S. Saitzek, Z. Shao, A. Bayart, A. Ferri, M. Huvé, P. Roussel, R. Desfeux, Journal of Materials Chemistry C, 2014, 2 (20), 4037 – 4043.

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