DYNAMIC CORRELATION-FUNCTION STUDIES OF THE MEDIUM-RANGE ORDER IN MATERIALS

This paper discusses the extraction of structural and dynamical inform ation from the Q-dependence of the dynamical structure factor, S(Q, E) , measured by inelastic neutron scattering. The analysis of data for v itreous SiO2 is considered, and it is shown that the Q-dependence of S (Q, E) may be investigated either in real space by use of a dynamic co rrelation function (DCF) or in reciprocal space by modelling. The mode lling approach provides a new means to extract the bond angle distribu tion, and the results obtained agree well with previous information on the bond angle distribution. The application of the DCF approach to d ata for a (crystalline) high T-c superconductor is used to show that t he DCF may provide partial structure factor information without isotop e substitution when the material contains elements with different mass es - a result with important potential for the study of amorphous mate rials.