Structure of non-crystalline materials

Intense synchrotron radiation X-ray techniques, combined with neutron methods, have been exploited to determine the complex architecture of non-crystalline materials. The complementary structural probes of X-ray Absorption Fine Structure (XAFS), X-ray Diffraction (XRD) and Small Angle X-ray Scattering (SAXS) have been directed at elucidating the atomic structure of silicate glasses and the physics underlying the formation of glass ceramics. By combining these measurements with neutron scattering performed at the Spallation Neutron Source at the Rutherford Appleton Laboratory, the powerful computational techniques of Reverse Monte Carlo and Molecular Dynamics are being exploited to determine three-dimensional structures in which the movement of ions responsible for electrical conductivity, chemical resistance and thermal expansion can be realistically studied.

Zeolites and their analogues are of major importance as the substrates for catalysis - their gigantic cavernous microporous structures can be doped with metals like Ni and Co to generate the microscopic centres for catalysis. Using combined synchrotron X-ray techniques, the local geometry of the metal centre have been followed in conjunction with the crystallography of the substrate as the catalyst is formed, begins to operate and eventually fails - unique experiments allowing the phenomenon of catalysis to be physically traced from birth to death. Inelastic neutron scattering experiments reveal not only the interatomic vibrations within the open network but also the low frequency modes that relate to the microporous structure - floppy modes which can also undermine the stability of the network, leading it to collapse to an amorphised phase of conventional density.