Structural, electronic, and magnetic properties of tungsten oxycarbides WC_1–xO_x and WO_3–xC_x from first principles calculations

Abstract

Ab initio total energy calculations using the full-potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) for the exchangecorrelation potential have been performed to predict the structural, cohesive, electronic, and magnetic properties for tungsten oxycarbides. Two possible stoichiometries have been considered: WC 1-x O x , formed by partial substitution of oxygen atoms for carbon in hexagonal WC, and WO 3-x C x , which appear in the carburization process of WO 3 . The optimized lattice parameters, theoretical density, cohesive energies, as well as electronic densities of states have been obtained and analyzed for the first time. We have found that these two systems differ substantially: WC 1-x O x behave as d metals, whereas WO 3-x C x behave as sp metals. The unexpected d 0 -magnetism due to the C 2p #" spin splitting for some WO 3-x C x solid solutions (SSs) was predicted. The chemical composition and O/C atomic ordering type are two main factors responsible for the properties of these materials.

Simulation of structural and electronic properties of amorphous tungsten oxycarbides

“…Next, we address the problem of predicting crystalline tungsten oxycarbides. This has recently been discussed by Suetin et al [14] for the examples WC oxygen atoms in WO 3 by carbon atoms and relax the resulting structure candidates using the full potential linearized augmented plane wave basis set. We verified that the structure of WC 0.5 O 0.5 with alternating layers of WC and WO ( figure 1 (left)) is indeed the optimal structure also when relaxing different structure candidates using VASP.…”

“…This methodology has indeed been successful in predicting the structure of Pt 2 Si 3 derived from Pt 2 Sn 3 [13]. A similar procedure for tungsten oxycarbides has been adapted by Suetin et al, who investigated the structure, electronic and magnetic properties of some tungsten oxycarbides by constructing approximate crystal structures obtained from systematically replacing the carbon by oxygen in the hexagonal structure of WC and oxygen by carbon in the cubic structure WO 3 [14]. However, a powerful evolutionary algorithm was recently proposed, which, in principle, can predict the crystal structure of materials with any atomic composition and is not biased by the choice of the initially known crystal structure settings [15][16][17].…”

Ab initio probing of the electronic band structure and Fermi surface of fluorine-doped WO3 as a novel low-T C superconductor

“…5 . We see that after the partial substitution of fluorine for oxygen, owing to the growth of electronic concentration (EC), the Fermi level (E F ) is shifted upward (compared with insulating WO 3 [13][14][15][16][17]) into the bottom of conduction band, leading to the metallic-like behavior of cubic WO 2.5 F 0.5 . The electronic states on the Fermi level and around it (from -1 eV to +2 eV) are mostly formed by W 5d orbitals, whereas the O 2p orbitals are in the range from -2 eV up to -11.5 eV.…”

“…We carried out a Bader [19] analysis, and the calculated effective atomic charges Q for ideal WO 3 the effective atomic charges decrease, but in general the inter-atomic charge transfer is much smaller than it is predicted in the aforementioned idealized ionic model. This can be explained by the peculiarities of inter-atomic bonding in WO 3 [13][14][15][16][17] and WO 2.5 F 0.5 , which is of a mixed ionic-covalent type, when, besides ionic bonding, moderate covalent W-O (W-F) interactions arise owing to hybridization of W 5d -O 2p (W 5d -F 2p) states, see Fig. 1.…”