Dopant occupancy and structural stability of doped lithium niobate crystals

On the basis of the bond valence model, an approach is established to determine the dopant occupancy in the lithium niobate (LN) crystallographic frame. The dopant location can be easily assigned by comparing the deviation of its normal and calculated valence states, when such a dopant is arbitrarily placed in both Li⁺ and Nb⁵⁺ sites, respectively. Further, the parameter Global Instability Index is used to characterize the structural instability of doped LN crystals. The dopant occupancy in the LN crystallographic frame and its interaction with the LN matrix are quantitatively understood by the structural stability. Calculated threshold values of various dopants are further obtained in the present work.