Liquid metal dynamics upon temperature increase: the experimental viewpoint

Liquid metals exist in a very wide temperature range and that property enables specific technological applications as well as allowing temperature dependent studies of fundamental properties in the liquid state. For some time now the liquid metal dynamics was investigated around the melting point in detail. Changes with rising temperature towards the boiling point were rarely in the focus of studies. Measurements on the microscopic dynamics of four classical monatomic liquid metals with increasing temperature demonstrate in the temperature range of about1.4Tmeltinga crossover in dynamics. Collective and single particle dynamics of liquid rubidium, lead, aluminium and gallium were scrutinized through scattering experiments and supporting molecular dynamics simulations. Structural relaxation dynamics, generalized viscosity, inelastic excitations and single particle dynamics demonstrate distinct and sometimes subtle changes with rising temperature. The liquid metal behaves in a viscous manner near the melting point and develops into a free-fluid state when a temperature range around1.4Tmis crossed. A calculation of the inherent structure energy of liquid aluminium supports this view within the potential energy landscape picture. The observation of changes in the reported four liquid metals with very different effective pair potentials suggests that the dynamic crossover might be universal for liquid metals.