Versatile Interplay of Chalcogenide and Dichalcogenide Anions in the Thiovanadate Ba7S(VS3O)2(S2)3 and Its Selenide Derivatives: Elaboration and DFT Meta-GGA Study.

ABSTRACT

Oxychalcogenides are emerging as promising alternative candidates for a variety of applications including for energy. Only few phases among them show the presence of Q-Q bonds (Q = chalcogenide anion) while they drastically alter the electronic structure and allow further structural flexibility. Four original oxy(poly)chalcogenide compounds in the system Ba-V-Q-O (Q = S, Se) were synthesized, characterized, and studied using density functional theory (DFT). The new structure type found for Ba7V2O2S13, which can be written as Ba7S(VS3O)2(S2)3, was substituted to yield three selenide derivatives Ba7V2O2S9.304Se3.696, Ba7V2O2S7.15Se5.85, and Ba7V2O2S6.85Se6.15. They represent original multiple-anion lattices and first members in the system Ba-V-Se-S-O. They exhibit in the first layer heteroleptic tetrahedra V5+S3O and isolated Q2- anions and in the second layer dichalcogenide pairs (Q2)2- with Q = S or Se. Selenide derivatives were attempted by targeting the selective substitution of isolated Q2- or (Q2)2- (in distinct layers) or both by selenide, but it systematically led to concomitant and partial substitution of both sites. A DFT meta-GGA study showed that selective substitution yields local constraints due to rigid VO3S and pairs. Experimentally, incorporation of selenide in both layers avoids geometrical mismatch and constraints. In such systems, we show that the interplay between the O/S anionic ratio around V5+, together with the presence/nature of the dichalcogenides (Q2)2- and isolated Q2-, impacts in unique manners the band gap and provides a rich background to tune the band gap and the symmetry.