Experimental and theoretical study of novel germanium tungstates compounds GexW1-xO3 (x ∼ 1/4, 1/2) and Ge1-xWO4 (x ∼ 0.2)

Abstract

The crystal structures of three (03) novel germanium tungstates were investigated by single-crystal X-ray diffraction and density functional theory (DFT) calculations. The structures are characterized by distorted MO6(M = Ge/W) octahedral, forming infinite zigzag chains.In GexW1-xO3(x ∼ 1/4, 1/2), the systems display a transition from pure WO3 semiconducting to metal-like behavior by shifting down the Fermi level; this is due to germanium's lower valence, which acts as a p-type semiconductor by creating electron holes in the lattice.It was found that GexW1-xO3(x ∼ 1/4, 1/2) exhibits strong reflectivity and absorption in the near-infrared region, while weak reflectivity and absorption appear in the visible region.Compared to GeWO4, the estimated electronic density of states in Ge1-xWO4(x ∼ 0.2) shows a narrow band gap (0.89 eV) due to Ge-vacancies, which is considered the smaller band gap among analogous wolframites, resulting in an increase of the absorption and the relectivity in the visible region.