Abstract
Pressure-induced polyamorphism in Ce-based metallic glass has attracted significant interest in condensed matter physics. In this paper, we discover that in association with the polyamorphism of La32Ce32Al16Ni5Cu15 bulk metallic glass, the acoustic velocities, measured up to 12.3 GPa using ultrasonic interferometry, exhibit velocity minima at 1.8 GPa for P wave and 3.2 GPa for S wave. The low and high density amorphous states are distinguished by their distinct pressure derivatives of the bulk and shear moduli. The elasticity, permanent densification, and polyamorphic transition are interpreted by the topological rearrangement of solute-centered clusters in medium-range order (MRO) mediated by the 4f electron delocalization of Ce under pressure. The precisely measured acoustic wave travel times which were used to derive the velocities and densities provided unprecedented data to document the evolution of the bulk and shear elastic moduli associated with a polyamorphic transition in La32Ce32Al16Ni5Cu15 bulk metallic glass and can shed new light on the mechanisms of polyamorphism and structural evolution in metallic glasses under pressure.
Highlights
Local atomic structure change are still obscure at present, especially for the shear wave velocity and shear modulus
The first sharp diffraction peak (FSDP), a ubiquitous feature in the x-ray diffraction patterns of amorphous materials, has been most widely used in probing structural variations of metallic glasses up to intermediate-range order (IRO) scale, as well as to estimate the bulk density under pressure in analogous to the use of Bragg peaks in their crystalline counterparts. It has been demonstrated recently by both experimental and theoretical studies that medium-range order (MRO) in BMGs displays fractal network characteristics, the atomic volume correlates with the position of the FSDP (q1) by a power-law relationship with a fractal dimensionality of 2.3–2.520–22, as compared to the cubic power relationship in crystalline solids
The relations between volume and pressure for metallic glasses have been mostly limited to assessments from analyses of the position of the first sharp diffraction peak (FSDP), with the assumption that the first peak position in momentum transfer (q1), sampling primarily MRO, correlates with the specific volume of glass by power law relationship[20, 21]
Summary
Local atomic structure change are still obscure at present, especially for the shear wave velocity and shear modulus. The first sharp diffraction peak (FSDP), a ubiquitous feature in the x-ray diffraction patterns of amorphous materials, has been most widely used in probing structural variations of metallic glasses up to intermediate-range order (IRO) scale, as well as to estimate the bulk density under pressure in analogous to the use of Bragg peaks in their crystalline counterparts It has been demonstrated recently by both experimental and theoretical studies that MRO in BMGs displays fractal network characteristics, the atomic volume correlates with the position of the FSDP (q1) by a power-law relationship with a fractal dimensionality of 2.3–2.520–22, as compared to the cubic power relationship in crystalline solids. Data from these unique techniques, together with previous data from X-ray diffraction, shed new light on the mechanism of polyamorphism in MGs from the perspective of structural ordering at various length scales
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