Chemical bonding in RFe6Ge4 (R = Li, Sc, Zr) and LuTi6Sn4 with rhombohedral LiFe6Ge4 type structure

• Published in: Solid state sciences 2015-01, Vol.39, p.82-91
• Main Authors: Matar, Samir F., Fickenscher, Thomas, Gerke, Birgit, Niehaus, Oliver, Rodewald, Ute Ch, Al Alam, Adel F., Ouaini, Naïm, Pöttgen, Rainer
• Format: Article
• Language: English
• Subjects: Bonding; Chemical bonding; Chemical Sciences; Construction; Germanides; Iron; Kagomé network; Lithium; Material chemistry; Mathematical analysis; Order disorder; Scandium; Stannides; Substructures
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2014.11.011

The germanide ScFe6Ge4 was synthesized from the elements by arc-melting. Its crystal structure was refined from single crystal X-ray diffractometer data: LiFe6Ge4 type, R3¯m, a = 507.9(3), c = 2000.9(1) pm, wR2 = 0.0737, 242 F2 values, 16 variables. The structure has two main building units. The iron atoms form double-layers of Kagomé networks (248–297 pm Fe–Fe) which are separated by layers of edge-sharing Sc@Ge8 hexagonal bipyramids (265–293 pm Sc–Ge). Chemical bonding has been studied based on DFT calculations for the AFe6Ge4 (A = Li, Sc, Zr) series and isotypic LuTi6Sn4. Existence of MgFe6Ge4 is proposed on the basis of full geometry optimization. Major differences are observed between the electronic structures and the magnetic properties and bonding of LuTi6Sn4 on the one hand and the AFe6Ge4 family on the other hand whereby the iron Kagomé substructure develops magnetization in all AFe6Ge4 compounds, in contrast to LuTi6Sn4. The Ti–Ti Kagomé substructure is found with bonding character throughout the valence band whereas Fe–Fe interactions are both bonding and antibonding with characteristic spin-dependent bonding. Spin-polarized calculations hint for magnetic ordering in the iron containing representatives. This was proven experimentally for ScFe6Ge4. Temperature-dependent susceptibility measurements show a Curie temperature of TC = 491(3) K. 57Fe Mössbauer spectroscopic measurements at ambient temperature show a single resonance at an isomer shift of 0.22(1) mm s−1 with a magnetic hyperfine field of 19.1(1) T. [Display omitted] •Synthesis and structural characterization of ScFe6Ge4.•Magnetic properties and 57Fe Mössbauer spectroscopy of ScFe6Ge4.•DFT calculations on the family of LiFe6Ge4 type intermetallics.