Atomic dynamics in the solid and liquid phases

Abstract

The objective of this thesis is to provide a better understanding of the dynamics of liquids. Dynamics are related to important properties of materials and can predict their behaviour. Theories of dynamics often study only crystalline systems and they do not involve other structural phases. Therefore it is important to understand the cor- relation of dynamics of the crystalline, amorphous and liquid phase. Understanding disordered systems can be facilitated if we understand their correlation with crystalline systems. In order to understand the connection on dynamics of the three phases I perform inelastic neutron scattering experiments and simulations. The inelastic neutron scattering is the best method to study high-frequency dynamics and obtain accurate results. I analyse and compare results from experiments and simulations for materials in their crystalline, amorphous and liquid phase. Further to the mi crostructure analysis of the three phases I analyse their local structure. I study possible memory e ffects in the short-range structure during phase changing and I discuss how these aff ect the dynamics of the system. Moreover I provide a theoretical explanation of the inter- atomic interactions in the local structure of crystals and I discuss the origin of the phononð€€€roton minimum that can be observed in phonon dispersion spectra of many materials. Finally I study macroscopic properties of the three phases on various materials, such as the heat capacity. The analysis and conclusions I present in this thesis provide a pioneer way of studying dynamics and they contribute to better understanding of unsolved fundamental physics questions. In this thesis I address and try to answer two major questions. To what extent the dynamic properties of solids and liquids can be compared at the microscopic and macroscopic level and how much the local structure a ffects dynamics.