Quantitative structural characterization of LiNbO3-SiO2 glass-ceramics by multinuclear solid-state NMR

This study presents a detailed structural analysis of the glass-to-crystal transition in the technologically important LiNbO ₃–SiO ₂ glass system, focusing on the composition 35Li ₂O–25Nb ₂O ₅–40SiO ₂ known for its exceptional second harmonic generation (SHG) response in glass-ceramics. We develop a comprehensive solid-state NMR protocol to quantify major and minor fractions of elusive nanocrystalline phases and the residual glass composition, overcoming limitations of techniques such as X-ray diffraction and Raman spectroscopy. By employing ⁷Li satellite transition difference spectroscopy and ⁹³Nb magic-angle spinning (MAS) NMR, we achieve quantification of crystalline fractions down to 1%. By combining all the complementary ⁶Li, ⁷Li, ²⁹Si, and ⁹³Nb MAS NMR experiments, we also deduce the composition of the residual glass. Short crystallization times (up to 120 min) at 640 °C result in nanocrystalline LiNbO ₃, whereas crystallization for 1440 min at this temperature additionally yields two Li ₂Si ₂O ₅ polymorphs and Li ₂SiO ₃. ⁷Li spin echo and ⁷Li{ ⁹³Nb} W-RESPDOR NMR spectroscopy indicate that LiNbO ₃ crystallizes in specific domains leaving behind SiO ₂-rich residual glassy domains. This work offers a time-efficient and versatile NMR protocol for characterizing crystalline and residual glass components in nanocrystalline glass-ceramics in the LiNbO ₃–SiO ₂ system and beyond, providing valuable insights into the crystallization process which is not possible with other techniques.