Results of local-density linear muffin-tin orbital (LMTO) electronic-structure calculations for both known and recently obtained niobium oxide phases with different crystal lattices and different coordination of Nb atoms are presented. Perovskite-like compounds with one- or two-dimensional Nb-O condensed clusters, as well as hexagonal layered structures with trigonal-prismatic coordination of Nb atoms, are used. For SrNbO3, BaNb5O8, BaNb4O6, and Sr2Nb5O9, the Fermi level is located at the shoulder of the Nb d conduction band with a low density of oxygen states. For hexagonal MxNbO2 (M=Li,Na) compounds, oxygen contributions definitely appear at EF, but remain small compared with those of the high-Tc superconducting cuprates. Pair-interaction energies and superexchange-interaction parameters were calculated using the LMTO Green-function method. Typical for high-Tc superconductors, antiferromagnetic coupling between metal atoms in the Nb-O planes is shown to exist, but not the ferromagnetic exchange between metal d and oxygen p states. The calculations show that perovskite niobium oxide systems are not good candidates in the search for new high-Tc superconducting materials, but that hexagonal layered niobium oxide phases of the type considered in this paper might be of interest in studies of low Tc superconducting oxides.
ASJC Scopus subject areas
- Condensed Matter Physics