Prediction of unusual stable ordered structures of Au-Pd alloys via a first-principles cluster expansion
- National Renewable Energy Laboratory, Golden, Colorado 80201 (United States)
- Universitaet Erlangen-Nuernberg (Germany)
We describe an iterative procedure which yields an accurate cluster expansion for Au-Pd using only a limited number of ab initio formation enthalpies. Our procedure addresses two problems: (a) given the local-density-approximation (LDA) formation energies for a fixed set of structures, it finds the pair and many-body cluster interactions best able to predict the formation energies of new structures, and (b) given such pair and many-body interactions, it augments the LDA set of 'input structures' by identifying additional structures that carry most information not yet included in the 'input'. Neither step can be done by intuitive selection. Using methods including genetic algorithm and statistical analysis to iteratively solve these problems, we build a cluster expansion able to predict the formation enthalpy of an arbitrary fcc lattice configuration with precision comparable to that of ab initio calculations themselves. We also study possible competing non-fcc structures of Au-Pd, using the results of a 'data mining' study. We then address the unresolved problem of bulk ordering in Au-Pd. Experimentally, the phase diagram of Au-Pd shows only a disordered solid solution. Even though the mixing enthalpy is negative, implying ordering, no ordered bulk phases have been detected. Thin film growth shows L1{sub 2}-ordered structures with composition Au{sub 3}Pd and AuPd{sub 3} and L1{sub 0} structure with composition AuPd. We find that (i) all the ground states of Au-Pd are fcc structures; (ii) the low-T ordered states of bulk Au-Pd are different from those observed experimentally in thin films; specifically, the ordered bulk Au{sub 3}Pd is stable in D0{sub 23} structure and and AuPd in chalcopyritelike Au{sub 2}Pd{sub 2} (201) superlattice structure, whereas thin films are seen in the L1{sub 2} and L1{sub 0} structures; (iii) AuPd{sub 3} L1{sub 2} is stable and does not phase separate, contrary to the suggestions of an earlier investigation; (iv) at compositions around Au{sub 3}Pd, we find several long-period superstructures (LPS's) to be stable, specifically, the one-dimensional LPS D0{sub 23} at composition Au{sub 3}Pd and two two-dimensional LPS's at compositions Au{sub 13}Pd{sub 4} and Au{sub 11}Pd{sub 4}; (v) Au-Pd has a number of unsuspected ground states, including the structure Au{sub 7}Pd{sub 5} with the lowest formation enthalpy and the (301) ''adaptive structures'' in the Au-rich composition range, all of which could not be predicted by other theoretical methods.
- OSTI ID:
- 20853341
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 74, Issue 3; Other Information: DOI: 10.1103/PhysRevB.74.035108; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
Similar Records
Electronic and geometric structure of transition-metal nanoclusters
Finding the Lowest-Energy Crystal Structure Starting From Randomly Selected Lattice Vectors and Atomic Positions: First Principles Evolutionary Study of the Au-Pd, Cd-Pt, Al-Sc, Cu-Pd, Pd-Ti, and Ir-N Binary Systems
Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACCURACY
ALGORITHMS
APPROXIMATIONS
CLUSTER EXPANSION
DENSITY FUNCTIONAL METHOD
FCC LATTICES
FORMATION HEAT
GOLD ALLOYS
GROUND STATES
ITERATIVE METHODS
MANY-BODY PROBLEM
MIXING HEAT
PALLADIUM ALLOYS
PHASE DIAGRAMS
SOLID SOLUTIONS
SUPERLATTICES
THIN FILMS