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Title: Structural Plasticity in the Frank‐Kasper Realm: Chemical Pressure Roles of the μ ‐ and χ‐Phase Units in the Mo−Fe−Cr System

Intermetallic phases have been known to exhibit a wide diversity since Pauling's seminal investigations into NaCd2in the 1920s that, along with Cd3Cu4and Mg2Al3, was shown by Samson to crystallize with a giant cubic cell containing >1000 atoms. The concept of structural plasticity – the notion that complex structures emerge from the release of internal stresses that would arise in simpler structures – has recently been used to account for one family of intermetallics, tracing the structures of Ca2Ag7, Ca14Cd51, CaPd5, and CaCd6to chemical pressure (CP) issues in the CaCu5type. Here, we extend the ideal of structural plasticity closer to the giant cells elucidated by Pauling and Samson through its application to a series of Mo−Fe−Cr Frank‐Kasper phases. We begin with a DFT‐CP analysis of the MgZn2‐type phase MoFe2, which serves as a parent structure toμ‐Mo6Fe7andχ‐Mo5Cr6Fe18. The analysis reveals negative CPs around the Mo atoms arising from collisions between the Fe atoms. Tighter Mo coordination is provided in theμ‐ orχ‐phases by substituting some of the Friauf polyhedra of MoFe2with eitherμ‐ andχ‐phase units, resulting in layers or blocks of Laves‐like connectivity. Sites preferences in theμ‐phase and the role of Cr substitution in theχ‐phase are explained through the dual lenses of CP and electronegativity. Parallels to the features of NaCd2hint that such giant‐unit‐celled intermetallics can represent striking manifestations of structural plasticity.

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Award ID(s):
Author(s) / Creator(s):
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Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Zeitschrift für anorganische und allgemeine Chemie
Page Range / eLocation ID:
p. 64-74
Medium: X
Sponsoring Org:
National Science Foundation
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