Computer-simulation studies of intrinsic defects inLiNbO3crystals

Abstract

We have performed an atomistic simulation study of the defect structure of ${\mathrm{LiNbO}}_3$ crystals resulting from ${\mathrm{Li}}_2$O deficiency and reduction treatments. ${\mathrm{Li}}_2$O excess is found to be unlikely in ${\mathrm{LiNbO}}_3$ crystals. It is shown that oxygen vacancies are not the dominant intrinsic defect species in ${\mathrm{LiNbO}}_3$. Important defects are (${\mathrm{Nb}}_{\mathrm{Li}{}^{4\mathrm{up}20.{\mathrm{V}}_{\mathrm{Nb}{}^{5\mathcal{’}})\mathcal{’}}}}$ and isolated ${\mathrm{Nb}}_{\mathrm{Li}{}^{4\mathrm{up}20.}}$ antisites. Small regions of ${\mathrm{LiNbO}}_3$ with ilmenite-like cation-stacking sequence are likely to occur; thus (${\mathrm{Nb}}_{\mathrm{Li}{}^{4\mathrm{up}20.{\mathrm{V}}_{\mathrm{Nb}{}^{5\mathcal{’}})\mathcal{’}}}}$ defects in ${\mathrm{LiNbO}}_3$ should be interpreted as Li vacancies within ilmenite-like crystal regions. Li Frenkel disorder is energetically favorable. Finally we study charge–self-trapping centers, i.e., polarons and bipolarons.