title: Structure and reactivity with oxygen of Pr2NiO(4+δ): an in situ synchrotron X-ray powder diffraction study.
abstract: The promising SOFC cathode material Pr2NiO(4.22) has been studied in situ under a pure oxygen atmosphere from 25 to 950 °C by high resolution synchrotron X-ray powder diffraction. At room temperature (RT) δ = 0.22(1), the average crystal structure turns out to be monoclinic. The subtle monoclinic distortion (γ = 90.066(1)° at RT), retained up to 460 °C, is interpreted in terms of specific tilt schemes of the NiO6 octahedra. It is also shown that Pr2NiO(4.22) is incommensurately structurally modulated already at room temperature, in the same manner as the homologous cobaltate La2CoO(4.14). The phase transition to the High Temperature Tetragonal (HTT) phase was completed at 480 °C without any evidence for the Low Temperature Orthorhombic (LTO) phase allowing clarifying the phase diagram of this K2NiF4-type ternary oxide. Moreover, it turns out that above 800 °C, the HTT phase transforms reversibly into two coexisting isomorphous tetragonal phases. The incommensurate modulation subsists up to 950 °C, although modified concomitantly with the two abovementioned phase transformations. In addition, the role of kinetics on the decomposition process is highlighted through thermo-gravimetric analyses.
authors.affiliation: Institut des Sciences Chimiques de Rennes (ISCR), Equipe «Chimie du Solide et Matériaux», UMR CNRS N°6226, Université de Rennes 1, 263 Avenue du Général Leclerc, 35042 Rennes, France. Olivier.Hernandez@univ-rennes1.fr Carmelo.Prestipino@univ-rennes1.fr.
authors.forename: Thibault
authors.initials: T
authors.lastname: Broux
authors.forename: Carmelo
authors.initials: C
authors.lastname: Prestipino
authors.forename: Mona
authors.initials: M
authors.lastname: Bahout
authors.forename: Serge
authors.initials: S
authors.lastname: Paofai
authors.forename: Erik
authors.initials: E
authors.lastname: Elkaïm
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Vibhu
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Grenier
authors.forename: Aline
authors.initials: A
authors.lastname: Rougier
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Bassat
authors.forename: Olivier
authors.initials: O
authors.lastname: Hernandez