Size of defect clusters in lithium niobate single crystals

On the basis of the Li-site vacancy model, the non-stoichiometric defects in LN crystals, i.e., anti-site defects Nb-Li and corresponding lithium vacancy defects V-Li, were investigated by the bond valence model. According to the valence sum rule, 4 V-Li sites must emerge in the nearest lattices of Nb-Li, and thus form a neutral cluster with the center, Nb-Li(V-Li)(4)Nb5O15. The bond graph of the defect cluster was given, which reveals the ideal chemical bonding characteristics of defect clusters. Combining the possible configuration of defect clusters and the ideal bond lengths in the bond graph, the size of defect clusters in the LN crystallographic frame is estimated as 0.9 similar to 1.2 nm in diameter.