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Infrared furnace for in situ neutron single‐crystal diffraction studies in controlled gas atmospheres at high temperatures
Author(s) -
Magro Fernando,
Ceretti Monica,
Meven Martin,
Paulus Werner
Publication year - 2021
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576721003198
Subject(s) - neutron diffraction , partial pressure , stoichiometry , single crystal , oxygen , bar (unit) , analytical chemistry (journal) , materials science , chemistry , crystallography , crystal structure , physics , organic chemistry , chromatography , meteorology
To understand oxygen diffusion mechanisms in non‐stoichiometric oxides, the possibility to explore structural changes as a function of the oxygen partial pressure with temperature and related oxygen bulk stoichiometry is mandatory. This article reports on the realization of a high‐temperature furnace, suitable for single‐crystal neutron diffraction, working continuously at temperatures of up to 1000°C at different and adjustable partial gas pressures of up to 2 bar (1 bar = 100 kPa). This allows exploration of the phase diagrams of non‐stoichiometric oxides under in situ conditions and controlled oxygen partial pressure. As a pilot study, the structural changes of Pr 2 NiO 4+δ were explored at room temperature (δ ≃ 0.24) and at 900°C under 1 bar P (O 2 ) (δ ≃ 0.13) as well as under secondary vacuum (approximately 10 −5 mbar) conditions yielding a δ close to zero. The strong anharmonic displacements of the apical oxygen atoms along the [110] shallow diffusion pathway, which were previously observed at room temperature and 400°C, become more isotropic at 900°C. The study shows that the anisotropic oxygen displacements, here related to lattice instabilities, play a major role in understanding oxygen diffusion pathways and related activation energies at moderate temperatures. This also shows the importance of the availability of reaction cells for single‐crystal neutron diffraction to explore the phase diagram and associated structural changes of non‐stoichiometric oxygen ion conductors and respective diffusion mechanisms.