The reaction of '70-labelled water with titanium n-propoxide [T~(OPT")~] proceeds rapidly to produce OTi, and OTi, environments that can be clearly identified from 1 7 0 magic-angle spinning NMR spectra. The gel structure is highly disordered but the quadrupolar interaction is shown to be small throughout (quadrupolar coupling constant, C,< 1.5 MHz). Organic fragments, which can be monitored by 13C NMR, remain right up until crystallisation of anatase at 300 "C. Crystallisation is confirmed by electron diffraction, and electron microscopy determines the crystallite size to be ca. 3 nm. 170 NMR and electron diffraction are also used to follow the conversion of anatase to rutile. Keywords Sol-gel processing ; Titania ; 1 7 0 MAS NMR ; Electron diffraction Sol-gel processing is becoming increasingly important in the formation of oxide precursors for the manufacture of dense ceramics' and high-surface-area samples.2 Hydrolysis of metal alkoxides can be controlled carefully to produce very fine Paper 3/01282D;
Large diamond particles up to 30μm in diameter have been deposited on W wire tips using Microwave Plasma Chemical Vapour Deposition. Raman, SEM and TEM investigations were all carried out on a single particle. Large growth steps were observed on (100) facets but were absent on the (111) facets. Raman measurements indicated greater crystalline quality for (100) than (111) facets. TEM revealed the (111) facets to be covered with small islands of diamond about 10Å high. The dominant defect was found to be stacking faulting on the {111} planes which gives rise to some hexagonal spacings in the electron diffraction pattern. The results suggest that growth in the <111> and <100> directions are driven by different mechanisms.
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