Abstract
Results of full-potential linear-muffin-tin-orbital calculations for the new intercalated niobium oxide phases and are presented. It is shown that alkali atoms are ionized, and their valence electrons completely fill the hybridized Nb d–O 2p conduction band in crystals making them semiconducting. In the nonstoichiometric phases, the Fermi level is located well inside the conduction band of predominant Nb 4d nature with significant contributions from O 2p states. Estimates of electron-phonon interaction parameters and in the scope of the rigid-ion approximation result in ∼12 K for and ∼9 K for in reasonable agreement with the experimental data—and show that superconductivity observed in these materials is of the usual electron-phonon type, similar to that in cubic . It is shown that the density of states at the Fermi level and for should be more critically dependent on stoichiometry than for . Since the electronic-structure peculiarities obtained in the calculations are very different than those typical for superconducting cuprates, it does not appear likely that any high- superconductors should be expected in this class of compounds.
- Received 19 July 1993
DOI:https://doi.org/10.1103/PhysRevB.49.15830
©1994 American Physical Society