2019-Sustainable Industrial Processing Summit
SIPS2019 Volume 3: Kobe Intl. Symp. / Science of Innovative and Sustainable Alloys and Magnets (SISAM)
| Editors: | F. Kongoli, M. Calin, J.M. Dubois, K. Zuzek-Rozman |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2019 |
| Pages: | 156 pages |
| ISBN: | 978-1-989820-02-5 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Comprehensive Modeling of Cu-Ni Nanoparticle Phase-Diagrams Based on Modified Cohesion and Coordination-Dependent Bond Energies
Micha Polak1; Leonid Rubinovich1;1BEN-GURION UNIVERSITY OF THE NEGEV, Beer-Sheva, Israel;
Type of Paper: Regular
Id Paper: 104
Topic: 42
Abstract:
Cu-Ni alloys have gained interest as bulk and nanoparticles (NPs) primarily due to their catalytic and magnetic properties. Different modeling methods employed before for computations of chemical-order were limited to Cu-Ni NPs consisting of few hundred atoms. The present study uses the highly efficient statistical-mechanical free-energy concentration expansion method (FCEM [1]), combined with coordination-dependent bond-energy variations (CBEV [2]), and the coarse-grained layer (CGLM [3]) models for the case of CuNi truncated-octahedrons (TO). This quite efficient semi-analytical methodology enables the exploration of chemical-order configurations and transitions between them in much larger particle sizes and over broad ranges of composition and temperature. Furthermore, in spite of free-atom electronic-relaxation contributions to transition-metal cohesive-energies, numerous studies have misused the latter instead of using genuine bond-energies in modeling NP properties [4].Using the corresponding modified cohesive-energies, and depending strongly on size and composition, the following findings regarding chemical-order configurations are obtained: due to the CBEV, asymmetric Janus-like configuration (JA) is expected to be the most stable for all compositions only for the 201, 586 and 1029-atom TO sizes. At elevated temperatures, they transform into quasi-mixed configurations (QM). For larger TOs, core-shell (CS) configurations start to stabilize in narrow ranges of elevated temperatures and intermediate compositions, and become progressively stable at increasingly wider ranges. Three types of transitions are revealed: JA-CS, CS-QM, and JA-QM, yielding the first comprehensive Cu-Ni nanophase-separation diagrams. The use of unmodified cohesive energies leads to significantly altered transition temperatures, demonstrating the importance of the commonly ignored modification. Preliminary results for Cu-Ni-Pd TOs reveal a considerable impact of Pd alloying on the chemical-order diagrams, particularly the suppression of JA in favor of CS configurations.
Keywords:
Alloys; Modeling; Nanocrystal; Nanoparticles;References:
[1] M. Polak and L. Rubinovich, Surf. Sci. Reports 38 (2000) 127-194.[2] L. Rubinovich and M. Polak, Phys. Rev. B 80 (2009) 045404.
[3] M. Polak and L. Rubinovich, Phys. Chem. Chem. Phys., 17 (2015) 28211-28218.
[4] M. Polak, L. Rubinovich, J. Phys.: Condens. Matter, 31 (2019) 215402.