Anomalous random correlations of force constants on the lattice dynamical properties of disordered Au-Fe alloys

Journal Article · 20 September 2017 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.96.100201 · OSTI ID:1417371

Kangsabanik, Jiban ^[1]; Chouhan, Rajiv K. ^[2]; Johnson, D. D. ^[3]; Alam, Aftab ^[1]

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1. Indian Institute of Technology Bombay, Mumbai (India)
2. Ames Lab., Ames, IA (United States)
3. Ames Lab. and Iowa State Univ., Ames, IA (United States)

Here, gold iron (Au-Fe) alloys are of immense interest due to their biocompatibility, anomalous Hall conductivity, and applications in various medical treatments. However, irrespective of the method of preparation, they often exhibit a high level of disorder with properties sensitive to the thermal or magnetic annealing temperatures. We calculate the lattice dynamical properties of Au_1–xFe_x alloys using density functional theory methods where, being multisite properties, reliable interatomic force constant (IFC) calculations in disordered alloys remain a challenge. We follow a twofold approach: an accurate IFC calculation in an environment with nominally zero chemical pair correlations to mimic the homogeneously disordered alloy and a configurational averaging for the desired phonon properties (e.g., dispersion, density of states, and entropy). We find an anomalous change in the IFC's and phonon dispersion (split bands) near x=0.19, which is attributed to the local stiffening of the Au-Au bonds when Au is in the vicinity of Fe. Other results based on mechanical and thermophysical properties reflect a similar anomaly: Phonon entropy, e.g., becomes negative below x=0.19, suggesting a tendency for chemical unmixing, reflecting the onset of a miscibility gap in the phase diagram. Our results match fairly well with reported data wherever available.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V); USDOE
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1417371
• Alternate ID(s): OSTI ID: 1393308
• Report Number(s): IS-J-9464; PRBMDO; TRN: US1801050
• Journal Information: Physical Review B, Vol. 96, Issue 10; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English