Hybrid density functional theory study of vanadium doping in stoichiometric and congruent LiNbO3

Abstract

The basic features of vanadium (V)-doped $\mathrm{LiNb}{\mathrm{O}}_{3}$, such as V doping sites, local lattice distortions, and electronic structures are investigated via hybrid density functional theory. The interaction between V and the intrinsic point defects is also studied in this work. V is found to prefer to substitute Li (${\mathrm{V}}_{\mathrm{Li}}$) at its highest charge state of +4 in most $\mathrm{LiNb}{\mathrm{O}}_{3}$ samples, and begins to substitute Nb to form a neutral ${\mathrm{V}}_{\mathrm{Nb}}$ defect as the Fermi level is increased. Furthermore, ${\mathrm{V}}_{\mathrm{Li}}$ exhibits different polaronic behaviors in stoichiometric and congruent $\mathrm{LiNb}{\mathrm{O}}_{3}$. The most stable ${\mathrm{V}}_{\mathrm{Li}}^{4+}$ tend to form a ${\mathrm{V}}_{\mathrm{Li}}^{2+}$ small bound polaron by simultaneously capturing two electrons in stoichiometric $\mathrm{LiNb}{\mathrm{O}}_{3}$, and form a bound bipolaron along the nonpolarization axis in the congruent samples. Moreover, both bound bipolarons along the polarization and nonpolarization axes are found in congruent $\mathrm{LiNb}{\mathrm{O}}_{3}$ by capturing two more electrons.