The electronic structure of tantalum oxynitride and the falsification of alpha-TaON

We have performed electronic structure calculations from first principles (LDA & GGA, plane waves & muffin-tin orbitals, pseudopotentials & all-electron techniques) on the two reported polymorphs of TaON. For the experimentally well-characterized beta-TaON adopting the baddeleyite structure type, there is excellent agreement between all accessible observables despite the supposedly correlated character of an oxynitride phase. Concerning hexagonal alpha-TaON proposed first in 1966, one finds tremendous contradictions between theory and experimentally reported data (molar volume, total energy differences, electronic transport etc.) In combination with the communicated X-ray diffraction diagram, alpha-TaON is considered an erroneous entry in the solid-state chemical literature that needs to be removed from the crystallographic databases.