Effect of Crystallization on Local Structure and Optical Properties of Glass with 12.5Li2O–50GeO2–37.5P2O5 Composition

The glass with a 12.5Li₂O–50GeO₂–37.5P₂O₅ composition was synthesized by melt quenching. Thermal annealing was used to obtain a single-phase LiGe₂(PO₄)₃ composition, which is promising as a solid electrolyte for all-solid-state lithium-ion power sources. By using full x-ray scattering with analysis of the pair distribution function, and diffuse reflectance spectroscopy in the UV-Vis range, the local structure and optical properties of initial (amorphous) glass and crystallized glass were studied. An assessment of the influence of glass crystallization on these properties was carried out. It was shown that structuring in the glass is observed only at the level of the first-second coordination sphere of Ge and P atoms. The presence of F⁺ centers in the glass was revealed in the optical absorption spectra of the initial glass; their concentration decreases as a result of glass crystallization. The estimated value of the band gap for the crystallized glass, i.e., for the LiGe₂(PO₄)₃ phase, is 6.15 eV for the case of direct allowed transitions, which exceeds the calculated value known from the literature by approximately 2 times.