Abstract
Physical and chemical properties have been studied in lithium niobate (LiNbO(3), LN) crystals grown by Czochralski from a boron doped melt. Optical uniformity and optical damage resistance of LiNbO(3):B crystals have been compared with control crystals of nominally pure congruent (CLN) and near-stoichiometric (NSLN K(2)O) composition. LiNbO(3):B crystals structure has been studied. Studied LiNbO(3):B crystals have been grown from differently synthesized charges. The charges have been synthesized from a mixture Nb(2)O(5):B-Li(2)CO(3) using homogeneously doped Nb(2)O(5):B precursor (sample 1, (B) = 0.0034 wt% in the charge) and by a direct solid phase synthesis from Nb(2)O(5)-Li(2)CO(3)-H(3)BO(3) mixture (sample 2, (B) = 0.0079 wt% in the charge). Only traces of boron (10(-5)-10(-4) wt%) have been detected in the samples. We have established that concentration of anti-site defects Nb(Li) is lower in both LiNbO(3):B than in CLN crystals. XRD analysis has confirmed that B(3+) cations localize in faces of tetrahedral voids O(4) of LN structure. The voids act as buffers at the anion sublattice distortion. Sample 1 has been shown to have a structure closer to NSLN K(2)O crystal than sample 2. We have also shown that the chemical purity of LN crystal increases compared to the melt purity because boron creates strong compounds with impurities in the melt system Li(2)O-Nb(2)O(5)-B(2)O(3). Metals impurities thus stay in the melt and do not transfer to the crystal.