Colloidal model systems for undercooled metallic melts

Kurzfassung

Due to their mesoscopic length scales, colloidal suspensions are ideal model systems to address fundamental issues in condensed matter physics such as liquid ordering, nucleation and crystallization. Colloidal particles are several orders of magnitude larger than atoms in metals and their relaxation behavior is very sluggish compared to atomic systems. Due to the possibility of tunable interaction, systematic investigations of the short-range order in a charged colloidal silica system far from equilibrium state are presented. Therefore, timedependent structure factors in the undercooled state were measured applying Ultra Small Angle X-ray Scattering. The results of these investigations are compared to measurements on metallic systems represented by an undercooled Ni melt applying neutron scattering. The measured structure factors of both physically different systems are analyzed using the same evaluation method which reveals icosahedral short-range order in the melt phase of both systems, colloids and pure metals as well. In addition, due to the variation of the interaction potential from soft repulsive to hard-sphere like bahavior, icosahedral short-range order is replaced by a fcc structure near the solid-fluid phase boundary.