Anionic polymeric bonds in nickel ditelluride: Crystal structure, and experimental and theoretical band structure

Nickel ditelluride was prepared in different ways. Single crystal X-ray investigations reveal that the products are always nonstoichometric with respect to the Ni content, Relatively short intra- and interslab Te-Te contacts are indicative of a polymeric network with multiple Te-Te bonds explaining the very low c/a value of 1.37 of the hexagonal cell, Experimental valence band spectra (UPS) confirm that NiTe2 is a metal, The emission at the Fermi level EF is due to Ni d and Te p states, This assignment is supported by the results of the calculated density of states curve (DOS) which demonstrates that Te p states contribute more than 50% to the DOS at E(F). Core level spectra (XPS) give evidence that Ni is in the paramagnetic Ni(II) (d(8)) state, The chemical shift of the Te 3d core level leads to the assignment of an oxidation state of - 1, in good agreement with the oxidation state of about - 1.2 deduced from the relation between the Te-Te distances versus oxidation states of the anion in (Te-2)(2-), Te2-. The three-dimensional character of NiTe2 deduced from the crystal structure is further confirmed by the calculated energy dispersion E(k). (C) 1996 Academic Press, Inc.