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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Cooling-Rate-Driven Polymorphism and Vacancy Ordering in Ce 2 MnGe 6 Intergrowth Phases

Intergrowth phases in intermetallic systems provide a compelling framework for investigating structure–property relationships as a function of crystallographic subunit stacking. In this study, we examine the influence of Mn vacancy ordering on subunit stacking and reassign the structure of Ce 2 MnGe 6 to a monoclinic C2/m space group (a = 8.3486(17) Å, b = 8.6181(18) Å, c = 10.778(2) Å, β = 101.17(2)°). Additionally, we report a monoclinic polymorph of the Ln 2 MGe 6 family characterized as a tripled c-axis supercell derivative of monoclinic Ce 2 MnGe 6 , 3×c-Ce 2 MnGe 6 (a = 8.3482(16) Å, b = 8.6179(18) Å, c = 31.813(6) Å, β = 93.763(7)°). This polymorph emerges under rapid cooling conditions during the synthesis and offers insight into the structural relationship between the orthorhombic and monoclinic variants of the Ln 2 MGe 6 phases. Notably, the supercell form of Ce 2 MnGe 6 (3×c-Ce 2 MnGe 6 ) exhibits increased electrical resistivity and suggests enhanced Zintl-like behavior, potentially indicating greater thermodynamic stability relative to the parent monoclinic phase.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(MnGe)2 by Materials Project

CeMn2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to eight equivalent Mn and eight equivalent Ge atoms. All Ce–Mn bond lengths are 3.36 Å. All Ce–Ge bond lengths are 3.11 Å. Mn is bonded to four equivalent Ce and four equivalent Ge atoms to form a mixture of face, edge, and corner-sharing MnCe4Ge4 tetrahedra. All Mn–Ge bond lengths are 2.44 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ce, four equivalent Mn, and one Ge atom. The Ge–Ge bond length is 2.62 Å.

36 MATERIALS SCIENCE↗