Y2ALGE3 - A SUPERCONDUCTIVE METALLIC ZINT L COMPOUND

Y2AlGe3 was prepared by heating the elements (950 degrees C) and inves tigated by means of single-crystal X-ray methods. The compound crystal lizes in a new structure (Pnma; a = 6.785(1) Angstrom, b = 4.189(1) An gstrom, c = 17.676(2) Angstrom; Z = 4) with a three-dimensional framew ork of Al and Ge atoms and with Y in the cavities. The AI atoms are su rrounded tetrahedrally by Ge atoms, which are arranged in the form of planar (Ge2-)(infinity) chains and isolated from each other respective ly. Although Y2AlGe3 is a metallic conductor and no valence compound, it achieves the structural requirements of Zintl's concept. This pictu re is supported by electrondensity and ELF calculations, which reveals covalent Al-Ge and Ge-Ge bondings, therefore Y2AlGe3 is interpreted a s a metallic Zintl-Compound, downplaying the metallic propertys. Y2AlG e3 becomes superconductively at 4.5 K. Isotypic compounds are found fo r Ln(2)AlGe(3) with Ln = Dy, Ho, Er, and Tm (For lattice constants see ''Inhaltsubersicht'').