Structural Features of the Extraordinary Low Glass Transition Temperature for Au₆₅Cu₁₈Si₁₇ Bulk Metallic Glass

Abstract

Au 65 Cu 18 Si 17 bulk metallic glass (BMG) exhibits an extraordinary low glass transition temperature (<100°C) and a wide supercooled liquid region. In order to elucidate the structural features of the extraordinary low glass transition temperature and high glass forming ability of the Au 65 Cu 18 Si 17 BMG, high-energy X-ray diffraction (HEXRD) and Extended X-ray Absorption Fine Structure (EXAFS) measurements were carried out using synchrotron radiation. A sharp first peak and oscillation of the structure factor S(Q) up to the high wave number Q can be attributed to the dominant weighting factor of the AuAu correlation over others. A reverse Monte Carlo (RMC) simulation was applied simultaneously to the HEXRD and EXAFS data. The obtained RMC model shows a quite highly dense packed structure with large amount of icosahedral type clusters around Au atoms while small ones around Si atoms. The partial CuCu pair distribution function g Cu,Cu (r) shows a sharp peak at a short interatomic distance, i.e., 2.38 ¡. The CuCu pairs with short interatomic distances and the large thermal fluctuation around Cu atoms are considered to be one of the structural characteristics of the low glass transition temperature of the Au 65 Cu 18 Si 17 BMG.

βrelaxation and low-temperature aging in a Au-based bulk metallic glass: From elastic properties to atomic-scale structure

“…At around 5Å, a splitting of the second G(r) peak is observed. This splitting has also been observed in a similar Au 65 Cu 18 Si 17 BMG alloy [37]. The positions of the two subpeaks R 21 and R 22 were determined by fitting with a sum of two Gaussians (see right inset in Fig.…”

“…(5); namely, the reduced height of the first structure factor maximum S(Q 1 )/S[Q 1 (T 0 )] and the reduced FWHM w/w(T 0 ). Other studies on BMG systems have shown these quantities to be useful as complementary metrics to the peak position [37,55,57]. In a single-component system, the FWHM can characterize the degree of ordering, where a broader FWHM indicates a more disordered state.…”

Partial structure investigation of the traditional bulk metallic glass Pd40Ni40P20

“…Such a trend is always observed, i.e., it is not a special properties in Pd 40 Ni 40 P 20 alloy, but is seen in metallic glasses in general. [45][46][47] To clarify the heterogeneity of the elemental concentrations quantitatively, the RMC simulation box with the length of 5.0807 nm was separated into 5 × 5 × 5 = 125 voxels, and the numbers of each element were counted. Figure 7 shows the atomic number distributions ξ i of (a) Pd, (b) Ni, (c) P, and (d) all atoms in voxels with the size of 1.0161 nm.…”

Reverse Monte Carlo modeling for local structures of noble metal nanoparticles using high-energy XRD and EXAFS

“…On the other hand, application of the RMC simulations for EXAFS data analysis has been rstly reported by Gurman and McGreevy 42 and several studies have been carried out for disordered molecular and nite-size systems, 43-51 e.g., bcc-Fe, 45 undercooled Cu 46 and Ni, 47 bulk metallic glasses, 48 binary oxide glasses, 49 liquid iodine, 50 and poly-atomic molecules in gas phase. 51 In contrast, RMC is rarely applied to discrete systems composed of molecules and small clusters.…”