17 O NMR investigation of hafnia and ternary hafnium oxides

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