Generalized-stacking-fault energy and twin-boundary energy of hexagonal close-packed Au: A first-principles calculation

Abstract

Although solid Au is usually most stable as a face-centered cubic (fcc) structure, pure hexagonal close-packed (hcp) Au has been successfully fabricated recently. However, the phase stability and mechanical property of this new material are unclear, which may restrict its further applications. Here we present the evidence that hcp → fcc phase transformation can proceed easily in Au by first-principles calculations. The extremely low generalized-stacking-fault (GSF) energy in the basal slip system implies a great tendency to form basal stacking faults, which opens the door to phase transformation from hcp to fcc. Moreover, the Au lattice extends slightly within the superficial layers due to the self-assembly of alkanethiolate species on hcp Au (0001) surface, which may also contribute to the hcp → fcc phase transformation. Compared with hcp Mg, the GSF energies for non-basal slip systems and the twin-boundary (TB) energies for and twins are larger in hcp Au, which indicates the more difficulty in generating non-basal stacking faults and twins. The findings provide new insights for understanding the nature of the hcp → fcc phase transformation and guide the experiments of fabricating and developing materials with new structures.

Ab initio molecular dynamics studies of Au38(SR)24 isomers under heating

“…Hence, when the SCH 2 CH 2 Ph ligands are replaced by SCH 3 the energy difference between the two isomers significantly drops (by up to 80-85%), indicating that large part of the stability of the Au 38Q structure arises from the disposition of the ligands around the prolate core. Furthermore, we found that the energy difference between the two Au 38 (SR) 24 isomers (in eV per atom) is of the same order of magnitude as the energy difference between the fcc and hcp phases of bulk gold calculated earlier using the DFT/PW91 level of theory [44].…”

“…Earlier, Wang et al [44] reported that the energy difference between fcc and hcp phases of gold calculated using DFT/PW91 is 1.9 meV per atom. Comparing the results of Wang et al with ours we find that the energy difference between the two forms of Au 38 (SR) 24 are of the same order of magnitude as the energy difference between the fcc phase and the metastable hcp phase of bulk gold.…”

Stability, electronic structure, and optical properties of protected gold-doped silver Ag29−xAux (x = 0–5) nanoclusters

“…In tables 1 and S1 (see According to DFT-based calculations, the energy difference between fcc-hcp and fcc-bcc phases of gold and silver are between 0.6-3.4 meV/atom [22][23][24][25] and 19-23 meV/atom, 22 respectively. Moreover, the hcp Au phase, which is stable under ambient conditions, transform to fcc phase on exposure to a transmission electron microscope beam.…”

“…These energy differences per atom are of the same order of magnitude as difference between the energy of the fcc (face-centred cubic) Au and the metastable hcp (hexagonal close-packed) Au phases. [22][23][24][25][26] Moreover, the comparison between the calculated and the experimental optical spectra indicates that main absorption features, such as the broadening and the blue-shift of the characteristic Ag 29 peak (at 447 nm), of the experimental spectra result from the contributions of the diverse Au-doped isomers co-existing in the synthesized mixture.…”

Controlled growth of hexagonal gold nanostructures during thermally induced self-assembling on Ge(001) surface

“…Nonetheless it was theoretically explored recently by Wang et al . 13 , who has shown the possibility of hcp to fcc phase transition by first principle calculations. The elastic constants for Au hcp were also calculated, confirming the possibility of fabricating pure and stable hcp Au under ambient conditions.…”