Polyamorphism of a Ce-based bulk metallic glass by high-pressure and high-temperature density measurements

Metallic glasses are of recent interest worldwide due to their remarkable physicochemical properties which can be put in relation with their crystalline counterparts. Among them, cerium-based metallic glasses (Ce-MGs) have unique features such as the existence of polyamorphism under pressure, which is unexpected in these spatially compact systems. While a phase transition between amorphous phases with change of density and local structure has been previously detected, the corresponding structural variation under pressure was not clearly identified due to difficulties in performing accurate measurements and reliable analysis. In this work, angle dispersive x-ray diffraction experiments of ${\mathrm{Ce}}₆₉{\mathrm{Al}}₁₀{\mathrm{Cu}}₂₀{\mathrm{Co}}₁$ bulk metallic glass have been performed up to 16 GPa along two distinct isotherms (300 and 340 K). All of the diffuse signals have then been processed in order to extract the structure factor $S(Q)$, the pair distribution $g(r)$, the atomic density $\ensuremath{\rho}$, and the compressibility as a function of pressure and temperature. These are crucial probes to fully characterize the phase diagram, and they clearly confirm the existence of a link between polyamorphism in Ce-MGs and the $\ensuremath{\gamma}$ $\ensuremath{\leftrightarrows}$ $\ensuremath{\alpha}$ transition in pure cerium. Finally, owing to the presence of a critical point in pure solid Ce, the existence of such a feature is discussed here for Ce-MGs.