Fluoridation of HfO₂

Abstract

Fluoridation of HfO2 was carried out with three commonly used solid-state fluoridation agents: PVDF, PTFE, and NH4HF2. Clear and reproducible differences are observed in the reaction products of the fluoropolymer reagents and NH4HF2 with the latter more readily reacting in air. Strong evidence of distinct, previously unreported hafnium oxyfluoride phases is produced by both reactions, and efforts to isolate them were successful for the air-NH4HF2 reaction. Synchrotron XRD, 19F NMR, and elemental analysis were employed to characterize the phase-pure material which appears to be analogous to known Zr–O–F phases with anion-deficient α-UO3 structures such as Zr7O9F10. Comparison with the hydrolysis of β-HfF4 under identical conditions depicts that the NH4HF2 route produces the oxyfluoride with greater selectivity and at lower temperatures. Thermodynamic calculations were employed to explain this result. Potential reaction pathways for the NH4HF2 fluoridation of HfO2 are discussed.

Perovskite-like K3TiOF5 Exhibits (3 + 1)-Dimensional Commensurate Structure Induced by Octahedrally Coordinated Potassium Ions

“…The intensity of the supercell reflections was much weaker than the intensity of the subcell reflections (see Figure a). Given the small contrast of the atomic structure factors between oxygen and fluorine, 19 F NMR spectroscopy was used to directly probe the number of fluorine sites and their local crystallographic environment. − The spectra are consistent with a local ratio of O:F = 1:5 in each Ti L 6 ( L = O, F) octahedron (see the following 19 F NMR discussion). This is also supported by charge balance considerations of the compound.…”

Biocompatible and Oxidation‐Resistant Ti3C2Tx MXene with Halogen‐Free Surface Terminations

“…However, since the halogen species are slowly released under basic conditions [26,27] or upon spontaneous oxidative degradation of the MXenes, [28][29][30][31] the presence of halogen terminations can limit the expandability of MXenes toward applications in semiconductor electronics and biomedical devices. For example, trace amounts of fluorine species, due to their strong reactivity, can degrade device components such as gate oxides [32][33][34] or metal electrodes, [35] leading to the device failure over longterm use. More importantly, for their sustainable use on biological interfaces, [36][37][38] fluorinated MXenes can raise safety concerns because the transudation of fluoride ions can be toxic to living organisms.…”

Controllable Syntheses, Crystal Structure Evolution, and Photoluminescence of Polymorphic Zirconium Oxyfluorides

“…15−20 Flynn et al reported the fluoridation of HfO 2 using PVDF, PTFE, and NH 4 HF 2 as solid-state fluoridation agents, which afforded either single-phase or multiple-phase hafnium oxyfluorides, respectively. 15 tion method has only been reported in limited several oxyfluoride systems until now. Further exploration and precise fluorination syntheses are needed for more functional metal oxyfluorides.…”

“…Low-temperature fluorination using metal oxides as raw materials is one of the typical methods. NH 4 HF 2 , polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE) are commonly used as the fluoridation agents in this method. − Flynn et al reported the fluoridation of HfO 2 using PVDF, PTFE, and NH 4 HF 2 as solid-state fluoridation agents, which afforded either single-phase or multiple-phase hafnium oxyfluorides, respectively . Hirai et al.…”