Volume Expansion Measurements in Metallic Liquids and Their Relation to Fragility and Glass Forming Ability: An Energy Landscape Interpretation

Recent studies of Cu-Zr glasses have reported a rapid variation in the amorphous phase density near the optimal glass forming compositions, supporting the belief that the densest liquids are also the best glass formers. Here, we show that the measured densities of the Cu-Zr liquids at higher temperatures are not peaked sharply near these compositions, but the volume expansivities are. Theoretical studies have shown that the expansivity correlates with fragility near T-g; the experimental results presented here show that at high temperature they become anticorrelated. From energy landscape arguments, this indicates the existence of a crossover temperature for the expansivity-fragility correlation that scales inversely with the liquid fragility. These results lead to an improved understanding of the high temperature properties of liquids that form glasses and suggest a new method for identifying the best glass forming compositions within an alloy system from the properties of the equilibrium liquids.