Electronic structure ofKNbO3andKTaO3

Abstract

The electronic structure of cubic KNb03 and KTa03 has been calculated using the self-consistent, scalar-relativistic linear-mufBn-tin-orbital method. The calculated density of states (DOS) shows a strong similarity for both materials and is in good accordance with measured photoelectron spectra (PES). The projected DOS reveals a strong d-band character for the valence band, which is due to an evident hybridization of 0 2p states with the unoccupied Nb(Ta) d states T. his is also confirmed by PES data, if one makes use of the Cooper minimum for d bands. The calculation underestimates the band gaps by about 5070, a result that is known also from other band calculations for insulators within density-functional theory. Ground-state properties are obtained &om totalenergy calculations. Lattice constants agree within a few percent with experimental ones. The bulk modulus for KTaOs (2.25 Mbar) is in good agreement with experiment, while for KNbOs (2.47 Mbar) it is nearly twice as large as the experimental value. Cohesive energies are found to be -42.2 eV for KNbOs and -44.5 eV for KTaOs (per unit cell). Corresponding experimental values do not seem to exist in standard literature.

First-principles studies of a two-dimensional electron gas at the interface in ferroelectric oxide heterostructures

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A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

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