skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures

Abstract

The classic metallurgical systems{emdash}noble-metal alloys{emdash}that have formed the benchmark for various alloy theories are revisited. First-principles fully relaxed general-potential linearized augmented plane-wave (LAPW) total energies of a few ordered structures are used as input to a mixed-space cluster expansion calculation to study the phase stability, thermodynamic properties, and bond lengths in Cu-Au, Ag-Au, Cu-Ag, and Ni-Au alloys. (i) Our theoretical calculations correctly reproduce the tendencies of Ag-Au and Cu-Au to form compounds and Ni-Au and Cu-Ag to phase separate at T=0 K. (ii) Of all possible structures, Cu{sub 3}Au (L1{sub 2}) and CuAu (L1{sub 0}) are found to be the most stable low-temperature phases of Cu{sub 1{minus}x}Au{sub x} with transition temperatures of 530 K and 660 K, respectively, compared to the experimental values 663 K and {approx}670 K. The significant improvement over previous first-principles studies is attributed to the more accurate treatment of atomic relaxations in the present work. (iii) LAPW formation enthalpies demonstrate that L1{sub 2}, the commonly assumed stable phase of CuAu{sub 3}, is {ital not} the ground state for Au-rich alloys, but rather that ordered (100) superlattices are stabilized. (iv) We extract the nonconfigurational (e.g., vibrational) entropies of formation and obtain large values for the size-mismatched systems:more » 0.48 k{sub B}/atom in Ni{sub 0.5}Au{sub 0.5} (T=1100 K), 0.37 k{sub B}/atom in Cu{sub 0.141}Ag{sub 0.859} (T=1052 K), and 0.16 k{sub B}/atom in Cu{sub 0.5}Au{sub 0.5} (T=800 K). (v) Using 8 atom/cell special quasirandom structures we study the bond lengths in disordered Cu-Au and Ni-Au alloys and obtain good qualitative agreement with recent extended x-ray-absorption fine-structure measurements. {copyright} {ital 1998} {ital The American Physical Society}« less

Authors:
; ;  [1]
  1. National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
Publication Date:
OSTI Identifier:
597205
Resource Type:
Journal Article
Journal Name:
Physical Review, B: Condensed Matter
Additional Journal Information:
Journal Volume: 57; Journal Issue: 11; Other Information: PBD: Mar 1998
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; FORMATION HEAT; NICKEL ALLOYS; COPPER ALLOYS; GOLD ALLOYS; SILVER ALLOYS; PHASE DIAGRAMS; CRYSTAL STRUCTURE; BOND LENGTHS; TRANSITION TEMPERATURE; TEMPERATURE RANGE 0400-1000 K; INTERMETALLIC COMPOUNDS

Citation Formats

Ozolins, V, Wolverton, C, and Zunger, A. Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures. United States: N. p., 1998. Web. doi:10.1103/PhysRevB.57.6427.
Ozolins, V, Wolverton, C, & Zunger, A. Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures. United States. https://doi.org/10.1103/PhysRevB.57.6427
Ozolins, V, Wolverton, C, and Zunger, A. Sun . "Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures". United States. https://doi.org/10.1103/PhysRevB.57.6427.
@article{osti_597205,
title = {Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures},
author = {Ozolins, V and Wolverton, C and Zunger, A},
abstractNote = {The classic metallurgical systems{emdash}noble-metal alloys{emdash}that have formed the benchmark for various alloy theories are revisited. First-principles fully relaxed general-potential linearized augmented plane-wave (LAPW) total energies of a few ordered structures are used as input to a mixed-space cluster expansion calculation to study the phase stability, thermodynamic properties, and bond lengths in Cu-Au, Ag-Au, Cu-Ag, and Ni-Au alloys. (i) Our theoretical calculations correctly reproduce the tendencies of Ag-Au and Cu-Au to form compounds and Ni-Au and Cu-Ag to phase separate at T=0 K. (ii) Of all possible structures, Cu{sub 3}Au (L1{sub 2}) and CuAu (L1{sub 0}) are found to be the most stable low-temperature phases of Cu{sub 1{minus}x}Au{sub x} with transition temperatures of 530 K and 660 K, respectively, compared to the experimental values 663 K and {approx}670 K. The significant improvement over previous first-principles studies is attributed to the more accurate treatment of atomic relaxations in the present work. (iii) LAPW formation enthalpies demonstrate that L1{sub 2}, the commonly assumed stable phase of CuAu{sub 3}, is {ital not} the ground state for Au-rich alloys, but rather that ordered (100) superlattices are stabilized. (iv) We extract the nonconfigurational (e.g., vibrational) entropies of formation and obtain large values for the size-mismatched systems: 0.48 k{sub B}/atom in Ni{sub 0.5}Au{sub 0.5} (T=1100 K), 0.37 k{sub B}/atom in Cu{sub 0.141}Ag{sub 0.859} (T=1052 K), and 0.16 k{sub B}/atom in Cu{sub 0.5}Au{sub 0.5} (T=800 K). (v) Using 8 atom/cell special quasirandom structures we study the bond lengths in disordered Cu-Au and Ni-Au alloys and obtain good qualitative agreement with recent extended x-ray-absorption fine-structure measurements. {copyright} {ital 1998} {ital The American Physical Society}},
doi = {10.1103/PhysRevB.57.6427},
url = {https://www.osti.gov/biblio/597205}, journal = {Physical Review, B: Condensed Matter},
number = 11,
volume = 57,
place = {United States},
year = {1998},
month = {3}
}