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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.

Single crystals of LiIn2SbO6 have been synthesized using a Li2MoO4 flux and characterized with X-ray diffraction. The compound crystallizes in a new structure-type with a rutile-related framework. ...

The anion-deficient fluorite-related family of materials exhibits a number of commercially useful properties arising from the specific arrangement of anion vacancies in each structure. One recently reported member, Zn0.456In1.084Ge0.46O3, is the only known example with its particular complex structure in which cation coordinations span one 4-coordinate (4b), two 6-coordinate (8e and 16f), and one 8-coordinate (4a) site. A new, complete, solid solution (CuxZn1–x)0.456In1.084Ge0.46O3, (0 ≤ x ≤ 1) has been discovered via the isovalent substitution of Cu2+ for Zn2+, significantly expanding the known phase space of this structure. Synchrotron X-ray data confirm the ZIGO structure over the entire composition range. Inclusion of Cu in the structure is found to occur exclusively at the 16f site, increasing the number of cations mixed on that site from three to four, while all others remain singly occupied, including the other 6-coordinate (8e) position. Furthermore, transmission electron microscopy investigations...

Indium and bismuth are technologically important elements, in particular as oxides for optoelectronic applications. 115In and 209Bi are both I = 9/2 nuclei with high natural abundances and moderately high frequencies but large nuclear electric quadrupole moments. Leveraging the quadrupolar interaction as a measure of local symmetry and polyhedral distortions for these nuclei could provide powerful insights on a range of applied materials. However, the absence of reported NMR parameters on these nuclei, particularly in oxides, hinders their use by the broader materials community. In this contribution, solid-state 115In and 209Bi NMR of three recently discovered quaternary bismuth or indium oxides are reported, supported by density functional theory calculations, numerical simulations, diffraction, and additional multinuclear (27Al, 69,71Ga, 121Sb) solid-state NMR measurements. The compounds LiIn2SbO6, BiAlTeO6, and BiGaTeO6 are measured without special equipment at 9.4 T, demonstrating that wideline techniques such as the QCPMG pulse sequence and frequency-stepped acquisition can enable straightforward extraction of quadrupolar tensor information in I = 9/2 115In and 209Bi even in sites with large quadrupolar coupling constants. Relationships are described between the NMR observables and local site symmetry. These are amongst the first reports of the NMR parameters of 115In, 121Sb, and 209Bi in oxides.

Elevated levels of fluoride (F(-)) in groundwaters of granitic and basaltic terrains pose a major environmental problem and are affecting millions of people all over the world. Hydroxyapatite (HA) has been shown to be a strong sorbent for F(-); however, low permeability of synthetic HA results in poor sorption efficiency. Here we provide a novel method of synthesizing nano- to micrometer sized HA on the surfaces of granular limestone to improve the sorption efficiency of the HA-based filter. Our experiments with granular limestone (38-63, 125-500 μm) and dissolved PO4(3-) (0.5-5.3 mM) as a function of pH (6-8) and temperature (25-80 °C) indicated rapid formation of nano- to micrometer sized HA crystals on granular limestone with the maximum surface coverage at lower pH and in the presence of multiple additions of aqueous PO4(3-). The HA crystal morphology varied with the above variables. The sorption kinetics and magnitude of F(-) sorption by HA-coated-fine limestone are comparable to those of pure HA, and the F(-) levels dropped to below the World Health Organization's drinking water limit of 79 μM for F(-) concentrations commonly encountered in contaminated potable waters, suggesting that these materials could be used as effective filters. Fluorine XANES spectra of synthetic HA reacted with F(-) suggest that the mode of sorption is through the formation of fluoridated-HA or fluorapatite at low F(-) levels and fluorite at high F(-) loadings.