Structure and Stability of TaON Polymorphs

Abstract

The stabilities and electronic structures of several polymorphs of tantalum oxynitride, TaON, were studied quantum-chemically at density-functional level. Results obtained by complementary quantum-chemical techniques with wave-functions either expanded in atom-centered functions or in plane waves were compared. Close agreement was obtained for the relative stabilities of the baddeleyite, anatase, rutile, and fluorite phases of TaON. The effect 1157 of anion distribution on the structural parameters and the lattice energies of the anatase and rutile polymorphs was investigated. The calculated band structure of the polymorphs is compared with available experimental information.

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

“…14 Possible anion arrangements have already been studied theoretically on a quantumchemical level 13 nitrides with anatase-type structure. Unfortunately, the amount of material (ca.…”

“…13 Since we used different density functionals in this work, we nevertheless performed structure re- The relative stability of the different anatase-type phases with respect to each other is linked to the N-N distance. In the most stable phase with I 41md symmetry, two N 3-ions are separated by at least 323 pm.…”

“…In addition, the relative stabilities of various structure types (including the anatase, rutile, and fluorite type) were calculated by quantum-chemical methods a couple of years ago. 13 Interestingly, and in clear contrast to TiO2, the anatase type is energetically favored compared to the rutile type. With the small calculated stability difference of only PUBLICATION 1 54 ca.…”

“…With the small calculated stability difference of only PUBLICATION 1 54 ca. 20 kJ·mol -1 between baddeleyite (most stable) and anatase type, 13 it is worth the effort trying to synthesize anatase-type TaON.…”

Synthesis and characterization of metastable transition metal oxides and oxide nitrides

“…Furthermore, quantum-chemical methods allow predictions of structural, thermodynamic and electronic properties for metastable phases that have not yet been synthesized. In previous studies [4,6,7] we have calculated fundamental band gaps of TaON polymorphs with hybrid functionals in order to account for the self-interaction error of standard density functional theory (DFT) using the semilocal generalized gradient approximation (GGA). The advantages and limitations of hybrid functionals for the study of the electronic properties of solid catalysts have been discussed recently [8].…”