Ilmenite-like stacking defect in nonstoichiometric lithium niobate crystals investigated by Raman scattering spectra

The Raman spectra of three pure lithium niobate (LiNbO3) crystals with diff erent content of Li and several doped LiNbO3 (Mg, In and Ti) crystals have been investigated. A weak peak at about 738 cm(-1) reported as a very stron g Raman peak of ilmenite phase LiNbO3 was observed for nonstoichiometric Li NbO3 crystals. The dependence of this peak on Li content and doping concent ration in crystal suggested that there is a new kind of defect structure wh ich has ilmenite-like stacking and direct relationship with antisite Nb-Li( 4+) ion. This result experimentally proved the existence of ilmenite-like s tacking defect in nonstoichiometric LiNbO3 for the first time. This defect is in good agreement with the Li vacancy model and has a different structur e from that proposed by Smyth [Ferroelectrics 50, 93 (1983); Proc. IEEE, p. 115 (1986)]. (C) 2000 American Institute of Physics. [S0021-8979(00)00907- 5].