Influence of Zn doping on electrooptical properties and structure parameters of lithium niobate crystals

We report the dependence of the unit cell parameters and the EO coefficients on Zn doping in optical damage-resistant LiNbO3:Zn crystals. Both properties depend in a non-monotonic manner on the Zn content. This is accounted for by different types of Zn ion incorporation into the lattice depending on the Zn concentration in the melt. Extrema observed in the concentration dependence of the EO coefficients at about 2-3 and 6.4 mol.% Zn correlate with an unusual concentration dependence of the unit cell parameters a and c. The low-concentration anomalies may be accounted for by a decrease of the Li vacancy concentration due to the Zn incorporation into Li sites. Anomalies at high concentrations are obviously due to a pal tial incorporation of Zn ions on Nb sites, which is reflected in the structure data. Anomalies in the concentration dependence of other optical properties at about 6-7 mol.% Zn reported recently are obviously related to a change in the localization of the Zn ions. The combination of high EO coefficients with a reduced optical damage for these concentrations make these crystals attractive for applications as Q-switching or electrooptical modulation.