Origin of pressure-induced polyamorphism in Ce75Al25 metallic glass.

Using high-pressure synchrotron x-ray absorption spectroscopy, we observed the Ce 4f electron in Ce(75)Al(25) metallic glass transform from its ambient localized state to an itinerant state above 5 GPa. A parallel x-ray diffraction study revealed a volume collapse of about 8.6%, coinciding with 4f delocalization. The transition started from a low-density state below 1.5 GPa, went through continuous densification ending with a high-density state above 5 GPa. This new type of electronic polyamorphism in densely packed metallic glass is dictated by the Ce constituent, and is fundamentally distinct from the well-established structural polyamorphism in which densification is caused by coordination change and atomic rearrangement.