ELECTRONIC-STRUCTURE AND ELECTRON-PHONON INTERACTIONS IN LAYERED LIXNBO2 AND NAXNBO2

Results of full-potential linear-muffin-tin-orbital calculations for t he new intercalated niobium oxide phases LixNbO2 and NaxNbO2 are prese nted. It is shown that alkali atoms are ionized, and their valence ele ctrons completely fill the hybridized Nb d-O 2p conduction band in M1. 0NbO2 CrystalS making them semiconducting. In the nonstoichiometric Mx NbO2 phases, the Fermi level is located well inside the conduction ban d of predominant Nb 4d nature with significant contributions from O 2p states. Estimates of electron-phonon interaction parameters and T(c) in the scope of the rigid-ion approximation result in T(c) approximate ly 12 K for Li0.5NbO2 and T(c) approximately 9 K for NaxNbO2 in reason able agreement with the experimental data-and show that superconductiv ity observed in these materials is of the usual electron-phonon type, similar to that in cubic Li0.5TiO2. It is shown that the density of st ates at the Fermi level and T(c) for NaxNbO2 should be more critically dependent on stoichiometry than for LixNbO2. Since the electronic-str ucture peculiarities obtained in the calculations are very different t han those typical for superconducting cuprates, it does not appear lik ely that any high-T(c) superconductors should be expected in this clas s of compounds.