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

Abstract

A series of perovskite-type phases of alkaline-earth-based tantalum and niobium oxynitrides has been studied using both first-principles electronic-structure calculations and molecular-dynamics simulations, in particular by investigating different structural arrangements and anion distributions in terms of total-energy calculations. The structural properties are explained on the basis of COHP chemical bonding analyses and semiempirical molecular orbital calculations. We provide theoretical proof for the surprising result that the local site symmetries of these phases are lower than cubic because density-functional calculations clearly show that all crystallographic unit cells are better described as being orthorhombic with space group Pmc2(1) to optimize metal-nitrogen bonding; nonetheless, there is no contradiction with a macroscopic cubic description of the structures of BaTaO(2)N and BaNbO(2)N adopting space group Pm3m. Additionally, we find that the anionic sublattice is ordered in all compounds studied over a wide temperature range.

Synthesis, Crystal Structure and Optical Properties of LaNbON2

“…The refinements were subject to the condition that each anionic site was fully occupied and that the overall anionic stoichiometry was equal to 3. The evaluation of the anionic occupancy factors resulted in the compositions LaNbO 1.02(5) N 1.98 (5) and LaNbO 1.03(5) N 1.97 (5) for the quenched and the slowly cooled oxynitride, respectively. These values are in good agreement with the composition obtained from the TGA and within the 1σ range correspond to the idealized composition LaNbON 2 .…”

“…ration (AB(O,N) 3 , B = Ti 4+ , Ta 5+ , Nb 5+ ) [3]. From recent DFT and electronic structure calculations [3][4][5] it follows that their electronic structure is related to that of early transition metal perovskite-type oxides such as, for example, KTaO 3 , SrTiO 3 : the top of the valence band is represented by the 2p-orbitals of the anions and the bottom of the conduction band is predominantly formed by the d-orbitals of the transition metals [6]. Despite of this general similarity, the incorporation of N 3-results in a pronounced change in energy of the frontier orbitals.…”

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

“…34 Therefore, we first calculated the quasiparticle gap with the GW0 method using the VASP code. [35][36][37][38] The computational setup for these surface calculations has been described in detail elsewhere. 39 For these calculations, we used small-core PAWs developed for GW calculations as supplied with the VASP program package.…”

Synthesis, structure and properties of new functional oxynitride ceramics

“…2(c). Such local symmetry reduction in SrTaO 2 N was already suggested by theoretical calculations 33) and EXAFS measurement, 16) because of a shorter TaN bond length than TaO. Local symmetry lowering was also suggested from electron diffraction analysis on SrTaO 2 N showing weak extra reflections that should be absent in the I4/mcm model.…”