Effect of disorder on thermodynamic instability of binary Rare-earth – Nickel – Palladium compounds

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Singh, Prashant
Del Rose, Tyler
Mudryk, Yaroslav
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Iowa State University Digital Repository, Ames IA (United States)
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

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Materials Science and Engineering

The Department of Materials Science and Engineering teaches the composition, microstructure, and processing of materials as well as their properties, uses, and performance. These fields of research utilize technologies in metals, ceramics, polymers, composites, and electronic materials.

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We have investigated the thermodynamic stability of disordered rare-earth phases SmX2 and Sm10X21 (X=Ni, Pd) using machine-learning based analytical descriptor and first-principles density functional theory methods. The absence of Laves phase compounds in R-Pd binary systems is a longstanding problem of rare earth science: even though Ni and Pd belong to the same group of the periodic table and have similar electronic structure, the Pd compound crystallizes in a monoclinic (C2/m) phase with 10:21 stoichiometry, i.e., Sm10Pd21, while the Ni compound adopts a cubic Laves phase (MgCu2) structure. To understand this contrasting phase stability, we performed thermodynamic convex hull analysis of SmxNi1-x and SmxPd1-x binary systems, which is experimentally validated using powder X-ray diffraction (PXRD) analyzes of polycrystalline Sm(NixPd1-x)2 samples with x=0, 0.5, and 1. A detailed electronic-structure (band-structure, charge density, and Fermi-surface) analysis of the differences between SmNi2/SmPd2 and Sm10Ni21/Sm10Pd21 compounds provides the quantum mechanical origin of the unfavorable mixing of Pd with Ni in cubic Laves phase. We show that the stability of Sm-Pd in 10:21 stoichiometry arises from improved intra-/inter-layer 5d-4d bonding compared to the 1:2 stoichiometry. Our work emphasizes the importance of ab-initio methods and computationally inexpensive analytical descriptors for the detailed analysis of thermodynamic and electronic properties of hard-to-prepare rare-earth compounds.
This is a manuscript of an article published as Singh, Prashant, Tyler Del Rose, and Yaroslav Mudryk. "Effect of disorder on thermodynamic instability of binary Rare-earth–Nickel–Palladium compounds." Acta Materialia 238 (2022): 118205. DOI: 10.1016/j.actamat.2022.118205. Copyright 2022 Acta Materialia Inc. Posted with permission. DOE Contract Number(s): AC02-07CH11358.