No abstract

Ferroelectric properties of Bi 1−x Pb x FeO 3 , through a structural approach, by structural Rietveld refinement and x-ray diffraction versus temperature have been carried out. This study allows us to draw a phase diagram for the system Bi 1−x Pb x FeO 3 . Although lead atom gets a lone pair and is commonly understood as having a "ferroelectric" character, we report in this paper that adding of lead atom in the Bi subsystem of BiFeO 3 , destroys the long-range FE order induced by Bi lone pairs on contrary, and progressively breaks the ferroelectric ordering up to the point where the structure becomes cubic on average. The decreasing of T C with increasing Pb content also confirms that adding of Pb atoms destabilizes the ferroelectric rhombohedral order and stabilizes the cubic phase via a complex texture of mixed phases, occurring at a local scale.

We have developed a new method to study the oxygen surface exchange kinetics in oxide materials in the form of epitaxial thin films by analyzing subtle cell parameter variations induced by changes in the oxygen stoichiometry of the material. The method consists of continuously analyzing the X-ray diffraction pattern of particular film reflections with a linear X-ray fast detector in a static position, while exposing the sample to sudden changes in the pO 2 of the atmosphere at elevated temperatures. With this method, we have been able to follow cell parameter changes as small as 2.10 −4 Å in time intervals as short as 10 s in La 2 NiO 4+δ epitaxial films and La 2 NiO 4+δ /LaNiO 3−δ bilayers. This method provides a simpler and contactless tool for dynamically analyzing oxygen surface exchange kinetics and diffusion in transition metal oxide compounds, and complements other currently used techniques such as Electric Conductivity Relaxation (ECR) and Isotopic Exchange depth profiling (IEDP). In addition, this method is a unique tool to address oxygen transport across solid−solid interfaces in thin film heterostructures.