Effect of point defects on Curie temperature of lithium niobate

Abstract

AbstractThe effect of point defects on the Curie temperature (Tc) of LiNbO3 (LN) was investigated by combining Tc measurements with an analysis of the defect structures of LN doped with impurities having various valences. The data show that Tc of congruent LN increases with the impurity concentration up to around 3 and 2 mol% for divalent and trivalent impurities, respectively, whereas it decreases continuously with increased concentrations of tetravalent impurities. These Tc variations were examined with respect to the defect structures of impurity‐doped LN, which are expressed in the form chemical formulae using Kröger‐Vink notation. The defect structures of divalent and trivalent impurity‐doped LN are and , respectively (NbLi: Nb at Li sites; VLi: vacancies at Li sites, MLi: impurities at Li sites, and Li/Nb = the congruent ratio). The defect structure in the case of tetravalent impurities is . Analyses of the defect structures indicated that the NbLi concentration decreases with divalent or trivalent impurity doping, which increases Tc. In contrast, the NbLi concentration increases with tetravalent impurity doping, which decreases Tc. In addition, the divalent or trivalent impurity concentrations at which the NbLi concentration becomes zero were found to correspond to the concentrations at which Tc is maximized, suggesting that Tc of LN depends on the NbLi concentration.