Diffuse Scattering Study of Short-Range Order in Lead Zinc Niobate
A month or two ago Dr Ross Whitfield had his PhD thesis passed. As Ross’s principal supervisor, I was most pleased to see the thesis go through. Ross did some nice work on modelling diffuse scattering from lead zinc niobate (PbZn1/3Nb2/3O3). Diffuse scattering helps us understand subtle aspects of the structures of materials. As I’ve noted before, diffuse scattering gives us information about the crystal structure that more ‘conventional’ experiments don’t give us. It lets us see inside the average structure, and get a look at how the atoms are arranging themselves at a local level — or at least, it gives us more information on this than a regular experiment.
To try to explain, regular crystallography experiment gives the global average crystal structure. Diffuse scattering tells use something about two-body averages. So, say you have a binary alloy. That is, an alloy made of two different atoms, A and B. Say they are not going in in an ordered way — sometimes A follows B, sometimes not. This means that the average structure will just show a single atom on each site, and this single atom will be a ‘half A half B‘ atom (something that does not really exist). The diffuse scattering can help you work out if A atom tend to be surrounded by B atoms, or if they tend to clump together. If you like, the conventional experiment can tell you the probability that a single site is occupied by B (or A), where the diffuse can tell you the probability that a site will be occupied by B given that its neighbour is also B (or A). These are two-body properties. They don’t tell use everything, but they do give us more information.
Ross looked at PZN using these ideas, and helped advance our ability to model the data, collect the data and process the data. A well-rounded PhD!