Unusual volume change associated with crystallization in Ce-Ga-Cu bulk metallic glass

In the general concept of crystallization kinetics, the amorphous solid with a number of open spaces transforms into a thermodynamically stable crystal, being denser than the corresponding amorphous phase. However, we unambiguously show that Ce70Ga6Cu24 bulk metallic glass (BMG) exhibits volume expansion together with the density decrease upon crystallization in sharp contrast to other amorphous materials. This anomalous behavior is found to be explained by the formation of structurally loose interfaces among crystallites in the crystalline Ce70Ga6Cu24 in addition to the disappearance of Ce-concentrated densely-packed local structure originally located in the amorphous matrix of BMG.