CaFe2Ge2 with square-planar iron layers – Closing a gap in the row of CaT2Ge2 (T = Mn–Zn).

The intermetallic compound CaFe 2 Ge 2 has been synthesized by ball-milling a stoichiometric mixture of pre-melted "FeGe" alloy with elemental Ca and subsequent annealing in welded niobium ampoule in a resistance furnace. Its crystal structure has been investigated by powder X-ray diffraction method: ThCr 2 Si 2 structure type (space group I 4/ mmm, Z = 2), a = b = 3.99366(4) Å, c = 10.7060(1) Å. Like iron-based superconductors, the main structural motif in CaFe 2 Ge 2 is a square-planar layer of Fe atoms that are tetrahedrally coordinated by Ge atoms. The (Fe 2 Ge 2) layers are alternating along the c -axis with the layers of Ca2+ cations and are interconnected via Ge–Ge bonds, resulting in a three-dimensional (Fe 2 Ge 2)2– polyanionic framework. The topological analysis of the Electron Localization Function (ELF) confirms 3D character of (Fe 2 Ge 2) layers similar to reported 122 iron tetrelides YFe 2 Ge 2 and CaFe 2 Si 2. CaFe 2 Ge 2 fills the gap in the row of Ca T 2 Ge 2 (T = Mn–Zn), being a fully-substituted variant (Ge/As) of the well-known superconducting collapsed tetragonal CaFe 2 As 2. Magnetic measurements revealed the occurrence of ferromagnetic order in CaFe 2 Ge 2 below 50 K. CaFe 2 Ge 2 has been synthesized by an unconventional solid-state method. This iron germanide crystallizes in the ThCr 2 Si 2 structure type. CaFe 2 Ge 2 is a fully-substituted (As/Ge) variant of iron-pnictide superconductor CaFe 2 As 2 and isoelectronic to its uncollapsed form. CaFe 2 Ge 2 orders ferromagnetically below 50 K. Image 1 • New ternary iron-germanide CaFe 2 Ge 2 has been synthesized by an unconventional solid-state method. • CaFe 2 Ge 2 is a fully-substituted (As/Ge) variant of iron-pnictide superconductor CaFe 2 As 2 and isoelectronic to its uncollapsed form. • CaFe 2 Ge 2 orders ferromagnetically below 50 K. [ABSTRACT FROM AUTHOR]