Disorder, crystals and the forgotten parts of powder diffraction

Hard Condensed Matter Seminar: Dr. Matt Tucker, Oak Ridge National Laboratory

Many of the useful materials that make modern life possible are crystalline. Quartz keeps our watches on time, perovskites are widely used in consumer electronics and solid oxide fuel cells may help to power the future.

The importance of local structure and disorder in crystalline materials is increasingly being recognised as a key property of many functional materials. From negative thermal expansion to solid state amorphisation and the 'nanoscale' problem to improved fuel cell technology, a clear picture of the local atomic structure is essential to understanding these phenomena and solving the associated problems.

Total scattering, an extension of the powder diffraction method, is increasingly being used to study crystalline materials. The unique combination of Bragg and diffuse scattering can be used to determine both the average structure and the short-range fluctuations from this average within a single experiment. To maximise the structural information from such data, three-dimensional atomic models consistent with all aspects of the data are required.

Here I will give an introduction to a program and technique, RMCProfile^[1], that can help you get the most from this valuable data. I will then give several examples to illustrate the sort of useful information you can gain using the total scattering method.  

[1] RMCProfile: reverse Monte Carlo for polycrystalline materials M G Tucker, D A Keen, M T Dove, A L Goodwin, Q Hui J. Phys.-Condes. Matter 19 335218 (2007) – also more information and the program available at www.rmcprofile.org