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Description
LiNbO3 is a widely used nonlinear optical material for photonic and quantum devices, where Li vacancy critically affects optical loss and photorefractive degradation under high-power operation. However, its quantitative evaluation remains challenging due to the low sensitivity of X-ray-based techniques to light elements. In this work, we systematically investigate the composition-dependent structural and vibrational responses of LiNbO3 and establish a practical framework for indirect evaluation of Li vacancy. High-resolution neutron powder diffraction (HRPD) was employed to quantify the [Li]/[Nb] ratio, which was then correlated with X-ray diffraction (XRD) and Raman spectroscopy. Within the single-phase region, decreasing [Li]/[Nb] leads to lattice expansion and a systematic shift of diffraction peaks toward lower angles, with representative (006) and (110) peaks exhibiting linear correlations with composition. Raman analysis reveals mode-dependent frequency shifts and linewidth broadening, with the Full Width at Half Maximum (FWHM) values of both the A1[LO4] and E[TO1] modes exhibiting clear correlations with composition. These results demonstrate that accessible and non-destructive techniques such as XRD and Raman spectroscopy enable indirect evaluation of Li vacancy in LiNbO3, providing a practical approach for defect evaluation in photonic materials.
