Unveiling the Fluorination Pathway of Ruddlesden-Popper Oxyfluorides: A Comprehensive In Situ X-ray and Neutron...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Inorganic Synthesis

Background:

• Ruddlesden-Popper oxyfluorides possess unique properties but are challenging to synthesize due to low thermodynamic stability.
• Understanding the formation mechanism is key to optimizing synthesis and discovering new materials.

Purpose of the Study:

• To investigate the fluorination mechanism of La₂NiO₄ using poly(vinylidene fluoride) (PVDF).
• To elucidate the reaction pathway for synthesizing La₂NiO₃F₂ and La₂NiO₂.5F₃ oxyfluorides.
• To demonstrate the utility of in situ laboratory X-ray diffraction (XRD) for complex solid-state reactions.

Main Methods:

• In situ laboratory X-ray diffraction (XRD) to monitor the reaction in real-time.
• X-ray and neutron powder diffraction to determine crystal structures of intermediates.
• In situ neutron powder diffraction with a low-background sapphire cell.
• 19F Magic Angle Spinning (MAS) NMR spectroscopy to track fluoride ion and PVDF.
• Rietveld refinements to quantify phase evolution.

Main Results:

• Identified four distinct reaction intermediates during the fluorination of La₂NiO₄.
• Elucidated the crystal structures of these intermediates and the final oxyfluoride products.
• Determined the reaction pathway: La₂NiO₄ → Inter#1 → Inter#2 → Inter#3 → La₂NiO₃F₂.
• Observed an alternative pathway via Inter#4 to La₂NiO₂.5F₃ with excess PVDF.
• Successfully synthesized both La₂NiO₃F₂ and La₂NiO₂.5F₃ oxyfluorides.

Conclusions:

• Laboratory in situ XRD is a powerful tool for understanding complex fluorination mechanisms.
• This approach enables controlled synthesis of novel oxyfluorides with tailored properties.
• The findings advance solid-state synthesis beyond traditional trial-and-error methods.