Atomic structure of Mg-based metallic glasses from molecular dynamics and neutron diffraction

Abstract

We use a combination of classical molecular dynamics simulation and neutron diffraction to identify the atomic structure of five different Mg-Zn-Ca bulk metallic glasses, covering a range of compositions with substantially different behaviour when implanted in vitro. There is very good agreement between the structures obtained from computer simulation and those found experimentally. Bond lengths and the total correlation function do not change significantly with composition. The zinc and calcium bonding shows differences between composition: the distribution of Zn-Ca bond lengths becomes narrower with increasing Zn content, and the preference for Zn and Ca to avoid bonding to themselves or each other becomes less strong, and, for Zn-Ca, transforms into a positive preference to bond to each other. This transition occurs at about the same Zn content at which the behaviour on implantation changes, hinting at a possible structural connection. A very broad distribution of Voronoi polyhedra are also found, and this distribution broadens with increasing Zn content. The efficient cluster packing model, which is often used to describe the structure of bulk metallic glasses, was found not to describe these systems well.

Influence of Dielectric Screenings on Phonon Frequencies and Acoustic Properties of Pd-Based Bulk Metallic Glasses

“…However, the understanding of phonon dynamics and atomic structure configuration are essential for understanding their mechanical and thermal properties [6][7][8][9]. The phonon dynamics of metallic glasses have been studied experimentally [10][11] using neutron scattering. Theoretically computed phonon frequencies have been investigated by many researchers [12][13][14][15][16][17] for correlating them with mechanical and thermal properties in a variety of metallic glasses.…”

“…The value of β and δ can be determined using equations (8), (9), (10) and (11). The sound velocities for both Pd 40 Ni 10 Cu 30 P 20 and Pd 64 Ni 16 P 20 BMGs are estimated for the longitudinal mode ( with different dielectric screenings and transverse mode ( ) in the long wavelength region from the respective dispersion curves.…”

“…For the Pd 40 Ni 10 Cu 30 P 20 BMG, the experimental values of , and [2] are 172.60×10 9 Nm -2 , 35.50×10 9 Nm -2 and 9.259×10 3 kgm -3 respectively and for the Pd 64 Ni 16 P 20 BMG, the experimental values of , and [2,17] are taken as 172.00×10 9 Nm -2 , 32.80×10 9 Nm -2 and 10.08×10 3 kgm -3 respectively. The values of is calculated using the , the values of the respective force constants β and δ for both the BMGs are obtained by substituting the respective values of , and κ e in equations (8), (9), (10) and (11). Hence all the input parameters for computing phonon dispersion curves for both the BMGs are known and are listed in Table 1.…”

Phonon Dynamics and Acoustic and Thermodynamic Properties of Pt_57.5Cu_14.7Ni_5.3P_22.5 Bulk Metallic Glass

“…The understanding of phonon dynamics and micro-structural configuration of metallic glasses is essential for understanding their acoustic, elastic and thermal properties [2][3][4][5][6][7]. Experimentally, neutron scattering has been used to study the phonon frequencies of metallic glasses [8,9]. The theoretically computed phonon dispersion curves both for longitudinal and transverse modes have also been reported by computer simulation and recursion techniques [8][9][10][11][12][13] for a variety of metallic glasses.…”

“…Experimentally, neutron scattering has been used to study the phonon frequencies of metallic glasses [8,9]. The theoretically computed phonon dispersion curves both for longitudinal and transverse modes have also been reported by computer simulation and recursion techniques [8][9][10][11][12][13] for a variety of metallic glasses. Three main theoretical approaches, namely Hubbard and Beeby [14], Takeno and Goda [15] and that of Bhatia and Singh [4] are widely used for computing phonon frequencies of metallic glasses.…”