The Electronic Structure of Tantalum Oxynitride and the Falsification of α‐TaON

Abstract

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 β‐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 α‐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, α‐TaON is considered an erroneous entry in the solid‐state chemical literature that needs to be removed from the crystallographic databases.

First‐principles and molecular‐dynamics study of structure and bonding in perovskite‐type oxynitrides ABO2N (A = Ca, Sr, Ba; B = Ta, Nb)

“…In our earlier work, we have studied the electronic and structural properties of several tantalum oxynitride polymorphs [15][16][17][18] by theoretical (i.e., mostly density-functional) methods. In this contribution, we now turn to the more complicated oxynitrides with perovskitelike structures to present a comprehensive theoretical study of structure and bonding in the aforementioned alkaline-earth-based tantalum and niobium oxynitrides.…”

Synthesis and Crystal Structure of δ-TaON, a Metastable Polymorph of Tantalum Oxide Nitride

“…Another polymorph, α-TaON, was suggested by Buslaev et al 8 but disproved by quantum-chemical calculations. 9 A possible high-pressure modification was predicted independently by two different groups. 10,11 Pressures of more than ca.…”

Synthesis and characterization of metastable transition metal oxides and oxide nitrides

“…Crystallizing in the well-known monoclinic baddeleyit-type structure, it is the most stable phase in this system [38]. Reports of a nearly simultaneous discovered α-polymorph [39,40] have been rebutted by quantum-chemical calculations [41]. A high-pressure modification with cotunnite-type structure and nine-fold coordinated cations was predicted independently by two different groups [42,43] and synthesized by Woodhead et al [44].…”