Reduction of Sr2MnO4 investigated by high temperature in situ neutron powder diffraction under hydrogen flow
| Autor: | Thibault Broux, Colin Greaves, Serge Paofai, Thomas C. Hansen, Mona Bahout, Olivier Hernandez, Florent Tonus |
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| Přispěvatelé: | Institut des Sciences Chimiques de Rennes (ISCR), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Center for Genomic Medicine, Copenhagen University Hospital-Rigshospitalet [Copenhagen], Copenhagen University Hospital, Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS) |
| Jazyk: | angličtina |
| Rok vydání: | 2013 |
| Předmět: |
Phase transition
Chemistry Reducing atmosphere Analytical chemistry 02 engineering and technology Activation energy [CHIM.INOR]Chemical Sciences/Inorganic chemistry 010402 general chemistry 021001 nanoscience & nanotechnology 7. Clean energy 01 natural sciences Isothermal process 0104 chemical sciences Inorganic Chemistry Tetragonal crystal system Reaction rate constant Phase (matter) Physical and Theoretical Chemistry 0210 nano-technology Monoclinic crystal system |
| Zdroj: | Inorganic Chemistry Inorganic Chemistry, American Chemical Society, 2013, 52 (2), pp.1009-17. ⟨10.1021/ic302265f⟩ Inorganic Chemistry, 2013, 52 (2), pp.1009-17. ⟨10.1021/ic302265f⟩ |
| ISSN: | 0020-1669 1520-510X |
| DOI: | 10.1021/ic302265f⟩ |
| Popis: | International audience; This experiment emphasizes the first example of two-phase sequential Rietveld refinements throughout a solid/gas chemical reaction monitored by Neutron Powder Diffraction (NPD) at high temperature. The reduction of the n = 1 Ruddlesden-Popper (RP) oxide Sr(2)MnO(4) heated under a flow of 5% H(2)-He has been investigated throughout two heating/cooling cycles involving isothermal heating at 500 and 550 °C. Oxygen loss proceeds above T ∼ 470 °C and increases with temperature and time. When the oxygen deintercalated from the "MnO(2)" equatorial layers of the structure results in the Sr(2)MnO(3.69(2)) composition, the RP phase undergoes a first order I4/mmm → P2(1)/c, tetragonal to monoclinic phase transition as observed from time-resolved in situ NPD. The phase transition proceeds at 500 °C but is incomplete; the weight ratio of the P2(1)/c phase reaches ∼41% after 130 min of isothermal heating. The fraction of the monoclinic phase increases with increasing temperature and the phase transition is complete after 80 min of isothermal heating at 550 °C. The composition of the reduced material refined to Sr(2)MnO(3.55(1)) and does not vary on extended heating at 550 °C and subsequent cooling to room temperature (RT). The symmetry of Sr(2)MnO(3.55(1)) is monoclinic at 550 °C and therefore consistent with the RT structure determined previously for the Sr(2)MnO(3.64) composition obtained from ex situ reduction. Consequently, the stresses due to phase changes on heating/cooling in reducing atmosphere may be minimized. The rate constants for the reduction of Sr(2)MnO(4.00) determined from the evolution of weight ratio of the tetragonal and monoclinic phase in the time-resolved isothermal NPD data collected on the isotherms at 500 and 550 °C are k(500) = 0.110 × 10(-2) and k(550) = 0.516 × 10(-2) min(-1) giving an activation energy of ∼163 kJ mol(-1) for the oxygen deintercalation reaction. |
| Databáze: | OpenAIRE |
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