Abstract
Our exploration in vanadate selenites by using boric acid flux method has successfully lead into a new phase, namely, γ-V2Se2O9. Single crystal X-ray diffraction indicates its a new structure which crystallizes in monoclinic space group P21/c with a lattice parameter of a = 7.4857 (12) Å, b = 7.4388 (8) Å, c = 13.042 (2) Å, β = 106.619 (9)°. Its crystal structure features novel 2D electroneutral [V2Se2O9] layers composed of 1D [V2SeO9]4- chains that are further bridged by Se (1)O3 triangular pyramids. [V2SeO9]4- chain consist corner-sharing of VO6 and tridentate Se (2)O3. Unlike previously reported α- and β-V2Se2O9 with isolated [V4O18]16− tetramers, corner-sharing of VO6 octahedra lead into a 1D [V2O9]8- chain in γ-V2Se2O9. X-ray powder diffraction and thermal behavior analysis were performed to study its phase purity and thermal stability. Optical diffuse reflectance spectra associated with Tauc's fitting indicates a direct bandgap semiconductor with an energy value of 2.34 eV, which consistent with the theoretical prediction. As a compare, the electronic bandgaps of three polymorphs were studied and shows a sequence of α-V2Se2O9<β-V2Se2O9<γ-V2Se2O9. Density of states were also calculated to reveal the origin of the bandgaps and bond interactions.
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