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Large-scale oxygen order phase transitions and fast ordering kinetics at moderate temperatures in Nd 2 NiO 4+ δ electrodes.

Sumit Ranjan MaityMonica CerettiRuben De BarrosLukas KellerJürg ScheferAntonio CervellinoJose Alberto Rodríguez-VelamazánWerner Paulus
Published in: Materials advances (2022)
Non-stoichiometric 214-nickelates with Ruddlesden-Popper (RP) type frameworks emerged as potential candidates for mixed electronic/ionic conductors in the intermediate temperature range. In this work we investigated structural aspects of the oxygen ion mobility diffusion mechanisms in non-stoichiometric Nd 2 NiO 4+ δ nickelates by X-ray (laboratory and synchrotron) as well by neutron diffraction. Temperature dependent synchrotron powder diffraction revealed a phase diagram of unprecedented complexity, involving a series of highly organized, 3D modulated phases related to oxygen ordering below 800 K. All phase transitionsimply translational periodicities exceeding 100 Å, and are found to be of 1 st order, together with fast ordering kinetics. These surprising structural correlations, induced by the presence of interstitial oxygen atoms, suggest a collective phason-like oxygen diffusion mechanism together with dynamical contributions from the aperiodical lattice creating shallow diffusion pathways down to room temperature.
Keyphrases
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