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

Abstract

This study presents a detailed structural analysis of the glass-to-crystal transition in the technologically important LiNbO3–SiO2 glass system, focusing on the composition 35Li2O–25Nb2O5–40SiO2 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 LiNbO3, whereas crystallization for 1440 min at this temperature additionally yields two Li2Si2O5 polymorphs and Li2SiO3. 7Li spin echo and 7Li{93Nb} W-RESPDOR NMR spectroscopy indicate that LiNbO3 crystallizes in specific domains leaving behind SiO2-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 LiNbO3–SiO2 system and beyond, providing valuable insights into the crystallization process which is not possible with other techniques.