Crystal-Like Atomic Arrangement and Optical Properties of 25La₂O₃-75MoO₃ Binary Glasses Composed of Isolated MoO₄²

Transparent and brown La₂O₃-MoO₃ binary glasses were prepared in bulk form using a levitation technique. The glass-forming range was limited, with the primary composition being approximately 25 mol % La₂O₃. The 25La₂O₃-75MoO₃ glass exhibited a clear crystallization at 546 °C, while determining its glass transition temperature was difficult. Notably, despite its amorphous nature, the glass possessed a density and packing density comparable to those of crystalline La₂Mo₃O₁₂. X-ray absorption fine structure and Raman scattering analyses revealed that the glass structure closely resembles La₂Mo₃O₁₂ due to the presence of isolated MoO₄^2- units, whereas disordered atomic arrangement around La atoms was confirmed. The glass demonstrated transparency ranging from 378 to 5500 nm, and the refractive index at 1.0 μm was estimated to be 2.0. The optical bandgap energy was 3.46 eV, which was slightly smaller than that of La₂Mo₃O₁₂. Additionally, the glass displayed a transparent region ranging from 6.5 to 8.0 μm. This occurrence results from the decreased diversity of MoO units and connectivity of Mo-O-Mo, which resulted in the reduced overlap of multiphonon absorption. This glass formation, with its departure from conventional glass-forming rules, resulted in distinctive glasses with crystal-like atomic arrangements.