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Abstract 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. 

Polar metals are an intriguing class of materials that simultaneously host free carriers and polar structural distortions. Despite the name “polar metal,” however, most well-studied polar metals are poor electrical conductors. Here, we demonstrate the molecular beam epitaxial growth of LaPtSb and LaAuGe, two polar metal compounds whose electrical resistivity is an order of magnitude lower than the well studied oxide polar metals. These materials belong to a broad family of ABC intermetallics adopting the stuffed wurtzite structure, also known as hexagonal Heusler compounds. Scanning transmission electron microscopy reveals a polar structure with unidirectionally buckled BC (PtSb and AuGe) planes. Magnetotransport measurements demonstrate good metallic behavior with low residual resistivity (ρLaAuGe = 59.05 μΩ cm and ρLaAPtSb = 27.81 μΩ cm at 2 K) and high carrier density (nh ∼ 1021 cm−3). Photoemission spectroscopy measurements confirm the band metallicity and are in quantitative agreement with density functional theory (DFT) calculations. Through DFT-chemical pressure and crystal orbital Hamilton population analyses, the atomic packing factor is found to support the polar buckling of the structure although the degree of direct interlayer B–C bonding is limited by repulsion at the A–C contacts. When combined with predicted ferroelectric hexagonal Heuslers, these materials provide a new platform for fully epitaxial, multiferroic heterostructures.