17O NMR investigation of hafnia and ternary hafnium oxides

Abstract

Structural evolution in alkoxide-derived amorphous HfO₂ gels is followed by ¹⁷O magic angle spinning (MAS) NMR in ¹⁷O-enriched samples, with crystallisation being identified readily at 500 °C. A series of ¹⁷O-enriched alkali-metal and alkaline-earth-metal hafnates with sodium chloride- and perovskite-related structures are also examined by ¹⁷O MAS NMR spectroscopy. The number of oxygen resonances is related to the crystal structure. Comparison of ¹⁷O NMR data is made to isostructural zirconium-containing compounds with the isotropic chemical shifts (Hf/Zr) in the ratio 0.86 ± 0.02. ¹⁷O NMR data are also presented from HfO₂–SiO₂ and HfO₂–GeO₂ gel mixtures.