Whitmore, Lee; (2002) Surface studies of complex oxides. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The surfaces of two distinct crystalline oxide materials have been investigated using interatomic potential techniques. The hydroxylated (111) surface of siliceous faujasite has been found to have two possible surface structures with very similar surface and attachment energies. Both surfaces have been observed experimentally by others and this thesis shows that the two surfaces are calculated to be the most favourable from many different surface terminations. Further to this, the adsorption on this surface of benzene and para-xylene and also the penetration of this surface by those molecules has been studied, the first time such a study has been undertaken. Surface adsorption energies and barriers to molecular transport through the surface layer of the microporous crystal are reported. One surface affords adsorption positions and diffusion barriers equivalent to the bulk of the material and one surface has weaker adsorption sites and lower diffusion barriers. Both surfaces show a significantly larger barrier to transport out of the crystal host than they do to transport into the crystal. The primary surfaces of zinc oxide crystals have been investigated using a new interatomic potential which was created for the purpose. In particular, the (1010) surface has been studied in detail, including its common defect structures. The findings from this work resolve an apparent conflict between theoretical and experimental observations about this particular surface. A technique for investigating growth mechanisms on surfaces has been utilised to show that the inhibitor ion, hexacyanoferrateIII could potentially act as an inhibitor and an activator for growth on the (111) and (100) surfaces of NaCl. The transferability of the technique to the study of the growth of zeolite and oxide materials is investigated.

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