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 Pr₂NiO_4+δ were explored at room temperature (δ ≃ 0.24) and at 900°C under 1 bar P(O₂) (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.

中文翻译：

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用于在高温受控气体气氛中进行原位中子单晶衍射研究的红外炉

为了理解非化学计量氧化物中的氧扩散机制，必须探索结构变化作为氧分压随温度和相关氧体积化学计量的函数的可能性。本文报告了高温炉的实现，适用于单晶中子衍射，在高达 1000°C 的温度下在不同且可调节的高达 2 bar (1 bar = 100 kPa) 的气体分压下连续工作. 这允许在原位条件和受控氧分压下探索非化学计量氧化物的相图。作为初步研究，在室温 (δ ≃ 0.24) 和 900°C 下 1 bar P下探索了 Pr ₂ NiO _4+δ的结构变化(O ₂ ) (δ ≃ 0.13) 以及在二级真空（大约10 ^-5 毫巴）条件下产生接近于零的δ。先前在室温和 400°C 下观察到的顶端氧原子沿 [110] 浅扩散路径的强非谐位移在 900°C 时变得更加各向同性。该研究表明，与晶格不稳定性相关的各向异性氧位移在理解中等温度下的氧扩散途径和相关活化能方面发挥着重要作用。这也表明了单晶中子衍射反应池的重要性，以探索非化学计量氧离子导体的相图和相关结构变化以及各自的扩散机制。