Structural characterisation of the silica and alumina Zener pinning phases in nanocrystalline CeO2 by 29Si and 27Al nuclear magnetic resonance
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Nanocrystalline CeO2 samples have been manufactured using sol-gel techniques, containing either 15 % silica or 10 % alumina by weight to restrict growth of the ceria nanocrystals during annealing by Zener pinning. 29Si and 27Al MAS NMR have been used to investigate the structure of these pinning phases over a range of annealing temperatures up to 1000 °C, and their effect on the CeO2 morphology has been studied using electron microscopy. The silica pinning phase resulted in CeO2 nanocrystals of average diameter 19 nm after annealing at 1000 °C, whereas the alumina pinned nanocrystals grew to 88 nm at the same temperature. The silica pinning phase was found to contain a significant amount of inherent disorder indicated by the presence of lower n Qn species even after annealing at 1000 °C. The alumina phase was less successful at restricting the growth of the ceria nanocrystals, and tended to separate into larger agglomerations of amorphous alumina, which crystallised to a transition alumina phase at higher temperatures.
KeywordsNanocrystal Nanocrystalline Ceria CeO2 Zener pinning Nuclear magnetic resonance Restricting growth Sol-gel 29Si NMR 27Al NMR Silica Alumina Instrumentation
The EPSRC are thanked for funding the collaboration between Warwick and Kent on nanocrystalline materials through grants (GR/S61881 and GR/S61898). MES thanks both EPSRC and the University of Warwick for partial funding of NMR equipment at Warwick. Steve York is also thanked for his help with electron microscopy.
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