Structural, electronic properties and inter-atomic bonding in layered chalcogenide oxides LaMChO (where M = Cu, Ag, and Ch = S, Se) from FLAPW-GGA calculations

Using the first principles FLAPW-GGA method, comparative study of structural, electronic properties and of chemical bonding in four 1111-like chalcogenide oxides LaMChO (LaCuSO, LaCuSeO, LaAgSO, and LaAgSeO) with ZrCuSiAs-type structure was performed. Our studies showed that: (i) replacements of d metal atoms (Cu ↔ Ag) and chalcogen atoms (S ↔ Se) lead to anisotropic deformations of the crystal structure; this effect is related to strong anisotropy of inter-atomic bonds; (ii) all of the examined chalcogenide oxides are semiconducting; the band gap decreases both at S → Se and Cu → Ag substitutions; and (iii) the bonding in LaMChO phases can be classified as a high-anisotropic mixture of ionic and covalent contributions, where mixed covalent-ionic bonds take place inside [La2O2] and [M2Ch2] blocks, whereas between the adjacent [La2O2]/[M2Ch2] blocks, ionic bonds emerge owing to [La2O2] → [M2Ch2] charge transfer. Since the near-Fermi bands of LaMChO phases originate mainly from electronic states of [M2Ch2] blocks, we speculate that chemical substitutions inside these blocks can result in striking differences in electronic properties of these systems; therefore, this approach can be promising for significant enlargement of the functional properties of these materials.

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► Structural, electronic properties for series of layered LaMChO phases were examined.
► All chalcogenide oxides are semiconducting; the trends in the band gap are evaluated.
► Chemical bonding in LaMChO is of ionic-covalent type and is highly anisotropic.
► Substitutions in [M2Ch2] blocks seem a promising way for updating of the properties.