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Site structures and antisite defects of impurity-doped lithium niobate

Chihiro Koyama ,  Kensaku Maeda ,  Jun Nozawa ,  Kozo Fujiwara ,  Satoshi Uda 

Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan


Lithium niobate (LiNbO3: LN) is a piezoelectric material, and it has been used as nonlinear optical device. A crystal is grown from the congruent melt to obtain homogeneous composition. During the crystal growth, antisite defect (NbLi) is generated because of excess Nb in LN. The NbLi causes photorefractive damage, which hinders optical application of LN. Regarding this problem, Zhong et al. (1980) found that MgO doping increased the damage resistance. However, it has not been fully understood how doping of impurities such as MgO affects to the defect formation which lead to optical damage. In the present study, site structures and NbLi behavior have been investigated by measuring lattice constants and curie temperatures (Tc) of LNs with changing impurity concentration.  Lattice constants of congruent LN(c-LN) doped with respective impurities (MgO, ZnO, Fe2O3, TiO2, ZrO2) were measured by XRD. Site structure changes caused by impurity doping were analyzed with variation of lattice constants with impurities. The analyses show that Mg, Zn and Fe were incorporated into Li-site, which decreased NbLi, in contrast Zr and Ti were incorporated into Nb-site, which increased NbLi.  Tcs of impurity-doped LNs were measured by DSC with changing a composition of LN along with two different series of A and B. In A series, impurities were doped to stoichiometric LN keeping Nb2O5 concentration to be 50 mol%. In B series, they were doped to c-LN keeping Li/Nb to be constant. In A series, Tc didn’t change, in which Li/Nb changed and NbLi was constant. In B series, on the other hand, Tc changed, in which Li/Nb was constant and NbLi changed. Tc has been believed to depend on Li/Nb in the non-doped LN (O'Bryan et al. 1985). However, from these results, we can conclude that Tc of doped LN depends on NbLi concentration instead of Li/Nb. Measurement of lattice constants and Tc reveal that the NbLi to be decreased by doping of Mg, Zn and Fe whereas increased by Zr and Ti.


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Related papers

Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 7, by Chihiro Koyama
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-03 09:40
Revised:   2013-04-03 09:40