Electronic structure and vibrational entropies of fcc Au-Fe alloys

Journal Article · Tue Jan 01 00:00:00 EST 2013 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.87.014301· OSTI ID:1097469

Munoz, Jorge A. ^[1]; Lucas, Matthew ^[2]; Mauger, L ^[3]; Halevy, I ^[1]; Horwath, J ^[2]; Semiatin, S L ^[2]; Xiao, Yuming ^[4]; Stone, Matthew B ^[5]; Abernathy, Douglas L ^[5]; Fultz, B. ^[1]

---

1. California Institute of Technology, Pasadena
2. United States Air Force Research Laboratory, Wright-Patterson Air Force Base
3. California Institute of Technology, W. M. Keck Laboratory, Pasadena
4. Carnegie Institution of Washington
5. ORNL

Phonon density of states (DOS) curves were measured on alloys of face-centered-cubic (fcc) Au-Fe using nuclear resonant inelastic x-ray scattering (NRIXS) and inelastic neutron scattering (INS). The NRIXS and INS results were combined to obtain the total phonon DOS and the partial phonon DOS curves of Au and Fe atoms. The 57Fe partial phonon DOS of the dilute alloy Au0.97 57Fe0.03 shows a localized mode centered 4.3% above the cutoff energy of the phonons in pure Au. The Mannheim model for impurity modes accurately reproduced this partial phonon DOS using the fcc Au phonon DOS with a ratio of host-host to impurity-host force constants of 1.55. First-principles calculations validated the assumption of first-nearest-neighbor forces in the Mannheim model and gave a similar ratio of force constants. The high energy local mode broadens with increasing Fe composition, but this has a small effect on the composition dependence of the vibrational entropy. The main effect on the vibrational entropy of alloying comes from a stiffening of the Au partial phonon DOS with Fe concentration. This stiffening is attributed to two main effects: 1) an increase in electron density in the free-electron-like states, and 2) stronger sd-hybridization. These two effects are comparable in magnitude.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1097469
• Journal Information: Physical Review B, Vol. 87, Issue 1; ISSN 1098--0121
• Country of Publication: United States
• Language: English