Synthesis, crystal structure, phase relations and chemical bonding analysis of the new Nowotny chimney-ladder compound ZrBi1.62

ZrBi1.62 is a new compound crystallising with an incommensurate Nowotny chimney-ladder structure, which was refined from single crystal X-ray diffraction data using a four-dimensional formalism. The tetragonal unit cell has the lattice parameters a = 6.958(7)A(ngstrom), c = 3.460(3)A(ngstrom) and q = (0 0 0.382). The symmetry is described by the superspace group pair W:P4/nnc:q-lql-P:l4(1)/amd:l-1ss. The full phase relations of ZrBi1.62 were established with DTA and phase analysis by X-ray powder diffraction, showing that the compound is thermodynamically stable only in the limited temperature range of 740-820 deg C. The chemical bonding in ZrBi1.62 was analyzed using the electron localization function (ELF) for the 5-fold and the 13-fold approximants of the incommensurate structure. The attractors of the ELF are located near the shortest Zr-Bi contacts, showing a covalent interaction between the zirconium and the bismuth atoms. No indication was found for direct bonding within the Zr and Bi networks, which usually is assumed in the crystal structure description of chimney-ladder phases. The calculated electron density of states (DOS) indicates metallic behavior.