Pressure-induced amorphous-to-amorphous configuration change in Ca-Al metallic glasses

Abstract

Pressure-induced amorphous-to-amorphous configuration changes in Ca-Al metallic glasses (MGs) were studied by performing in-situ room-temperature high-pressure x-ray diffraction up to about 40 GPa. Changes in compressibility at about 18 GPa, 15.5 GPa and 7.5 GPa during compression are detected in Ca80Al20, Ca72.7Al27.3, and Ca66.4Al33.6 MGs, respectively, whereas no clear change has been detected in the Ca50Al50 MG. The transfer of s electrons into d orbitals under pressure, reported for the pressure-induced phase transformations in pure polycrystalline Ca, is suggested to explain the observation of an amorphous-to-amorphous configuration change in this Ca-Al MG system. Results presented here show that the pressure induced amorphous-to-amorphous configuration is not limited to f electron-containing MGs.

Composition-Dependent Structural and Electronic Properties of Mg95–xZnxCa5 Metallic Glasses: An Ab Initio Molecular Dynamics Study

“…It is also noted that the d orbital of Ca atoms is overwhelmingly dominant around the Fermi level, similar to the case of Ca−Al MGs. 67 The transfer of electrons from the 4s orbital to the empty 3d orbital of Ca can be due in part to the avoidance of s and p band crossing, 68 76 For clarity and ease of presentation, only half of the simulation box in the direction perpendicular to the paper is shown. It is seen that the electrons are mainly localized to Zn atoms and form into a continuous network at Zn-rich compositions.…”

Structural behaviour of Pd40Cu30Ni10P20 metallic glass under high pressure

“…The mechanism here is suggested to be related to delocalization of 4f electrons, which occurs in Ce under high pressure leading to bond shortening and volume collapse [5e7]. However, also for glassy CaeAl [8], Pd- [9], Zr- [10], Gd- [11], and Pr-based [11] bulk metallic glasses, polyamorphic transitions were reported. The occurrence of the phase transition was concluded from observation of kinks in the pressure shifts of the first diffuse X-ray diffraction (XRD) peak or from the deviation of the pressureevolume relations of the well-established fundamental thermodynamic equation of state (EOS) [12].…”

Polyamorphism in cerium based bulk metallic glasses: Electronic and structural properties under pressure and temperature by x-ray absorption techniques

“…a transition (large volume collapse, existence of a critical point (CP) at the end of this transition line, or an atypical mechanism 20 ), polyamorphism in Ce-BMGs is then expected to generate quite unusual important structural modifications. 21 Insight into the nature of this polyamorphism in terms of changes in the local structure or order of the transition is a remaining issue. Indeed, the "classical" amorphousamorphous structural phase transitions earlier reported in covalent glasses with low coordination number (CN) and directional bonding (ice, 22 silica 23 ) involves a topological rearrangement of atoms driven by an increase of CN under pressure.…”