Ba2NiTeO6 – eine neue Verbindung in der Reihe der hexagonalen Perowskite

Ba₂NiTeO₆ — a novel compound in the series of hexagonal perovskites (Ba₂)(¹²)(NiTe)(⁶)O₆ crystallizes in the rhombohedral space group R3 m with a = 5.797 and c = 28.595 Å for the unit cell in the trigonal setting, which contains 6 formula units. The crystal structure was solved by single crystal X-ray diffraction and refined down to R = 2.9%. It can be described by 12 close-packed BaO₃ layers alternating in the sequence hhcchhcc…, with an ordered occupation of the octahedral lattice sites by Ni and Te atoms. Groups of three octahedra, which are connected with one another by common faces, are linked with each other by TeO₆ octahedra via common corners. The central octahedra of these face-linked groups are occupied by Te, the outer ones by Ni. The bonding within the NiO₆ polyhedra is discussed on the basis of the ligand field spectra and compared to similar compounds. It is shown that there can be an appreciable change of the ligand field parameter Δ (30%) even when the Ni — O distances are nearly equal — in contrast to the predictions of the crystal field theory. Effects of this kind are observed under certain structural conditions, when the bonding within the NiO₆ polyhedra is changed indirectly by substitution of atoms with a noble gas configuration (W⁶⁺) by atoms with a d¹⁰-configuration (Te⁶⁺) in the cationic environment of Ni²⁺.