Structural changes of the metallic glass Zr65Al7.5Cu27.5 during glass transition and in the undercooled liquid region

Abstract

The metallic glass ${\mathrm{Zr}}_{\mathrm{65}}{\mathrm{Al}}_{\mathrm{7.5}}{\mathrm{Cu}}_{\mathrm{27.5}}$ exhibits a wide temperature range in the undercooled liquid region. This offers the possibility of examining the phenomena that occur during glass transition. We investigated this glass by x-ray diffraction and x-ray absorption spectroscopy (XAS) at room temperature and at elevated temperatures below and above the glass transition temperature. The total number of nearest neighbors determined by x-ray diffraction remained unchanged. Using XAS irreversible changes in the short range order (SRO) towards the SRO of crystalline ${\mathrm{Zr}}_{\mathrm{2}}\mathrm{Cu}$ is observed in the nearest neighbor shell which is consistent with the x-ray diffraction results. The long range order was not affected by these changes. From the temperature dependence of the atomic mean-square relative displacements ${\sigma }^2,$ Debye temperatures were determined and they compare well with low temperature specific heat measurements. Above $T_g$ the slope of ${\sigma }^2$ increases drastically and is attributed to anharmonic effects.