Crystal Structure and Theoretical Study of a Novel GermaniumTungstate GexW1-xO3 (x ~ 1/8)

Introduction: Tungsten trioxide (WO3) is an n-type semiconductor with remarkable properties, offering wide potential for applications in smart windows, energyefficient coatings, and optoelectronic devices. Cation substitution provides an effective approach to modulating its structural, electronic, and optical properties. This study reports the synthesis, structural characterization, and first-principles investigation of a novel germanium-substituted tungsten oxide, W1-xGexO3 (x ~ 1/8), focusing on the impact of Ge doping on its structural, electronic, and optical properties. Methods: Single crystals of W1-xGexO3 (x ~ 1/8) were synthesized via the Chemical Vapor Transport (CVT) method. Their crystal structure was determined using single-crystal X-ray diffraction, while Density Functional Theory (DFT) simulations were conducted to validate the thermodynamic stability of the doped phase and to provide further insights into its electronic and optical properties. Results: The compound crystallizes in a tetragonal structure consisting of distorted MO6 (M = Ge/W) octahedra forming zigzag chains. Ge incorporation reduces octahedral distortion and stabilizes the lattice. DFT calculations revealed a reduced band gap compared to pristine WO3, indicating a transition from semiconducting behavior toward a more metal-like character in the x ~ 1/8. Discussion: Optical characterization showed a redshifted absorption feature near 4.5 eV, enhanced transparency in the visible and Near-Infrared (NIR) regions, and a moderate dielectric response (ε1(0) = 5.63). The reflectivity reached a maximum of 60.5% in the UV region while remaining low in the visible-NIR range. Conclusion: Low-level Ge doping (x ~ 1/8) in WO3 stabilizes the structure, reduces octahedral distortion, and enables tunable electronic and optical properties. These properties make it a strong candidate for smart windows, energy-efficient coatings, and optoelectronic devices.