Neutron scattering methods to study the local structure of disordered crystals

地点: 沙河校区C座五层X Space

时间: 2024年7月12日，10：00

主讲人: Martin Dove 教授 四川大学

Abstract:

The experimental art of x-ray crystallography is just over 100 years old. It's successes are widespread in sciences, and of considerable impact on the modern world. Once we know the crystal structure of a material we may feel we know everything about where the atoms are, but in many cases this is not so, because many materials show some degree of disorder over short distances. In these cases the local structure may show significant fluctuations away from the average structure given by Bragg scattering. Standard diffraction can tell us very little about local structure, because it is only contains information about mean positions. On the other hand, methods based on "total scattering" can provide much more detailed information about local structure.

The best measurement of local structure is a technique called "total scattering". This is exactly what is suggested by its name: it is a the full scattering of radiation by a material, including Bragg scattering and the diffuse scattering that spans the whole range of scattering vectors. The Fourier transform of the total scattering gives the "pair distribution function" (PDF) which can be thought of as a histogram of all the instantaneous distances between atoms. The PDF is the ideal fingerprint of local structure.

In this talk I will briefly describe methods to measure the PDF, and then discuss in detail how we use the Reverse Monte Carlo method to use the PDF, total scattering and Bragg scattering to generate large configurations of atoms that are consistent with these data. These configurations are consistent with information about the average structure and the atomic fluctuations given in the data. Over time I have become convinced that the PDF + RMC method can give unique insights into the local structures of disordered crystalline materials. I will illustrate the methods by discussing a number of recent examples.

About speaker:

Prof. Dove received his Ph. D from University of Birmingham and carried out postdoctoral work at the University of Edinburgh and the University of Cambridge successively. He was appointed as a director to the National Institute for Environmental eScience in 2002 and was promoted to a full professor in 2003 at the University of Cambridge. From 2011, He worked at School of Physics and Astronomy, Queen Mary University of London and he has been the director of the Centre for Condensed Matter and Materials Physics. At present he is a full-time foreign professor at Sichuan University. He spends significant research effort in disordered materials and structure–property relationships. His research includes experimental work of neutron scattering and computer simulation, which mainly involves phase transitions, amorphous materials, negative thermal expansion and radiation damage. He is one of the first researchers to apply the Reverse Monte Carlo method to analyze scattering data of crystal materials and develops the RUM model to understand phase transitions and negative thermal expansion of network materials. He has won Philips Physical Crystallography Prize (British Crystallographic Association) in 1990. He was elected as the fellow of the UK Institute of Physics in 2003, rewarded an Alexander von Humboldt award in 2007.