Point defects substitution mechanism in indium-doped LiNbO3 single crystals revealed by UV–Visible and Micro-Raman analysis

Abstract

This work reveals relevant information about the mechanism of substitution of point defects by In ions in lithium niobate single crystals doped with In in moderate concentrations ranging from 0.5 to 4 mol % in the melt. It was found that the In ions, first replace Nb ions at Li sites, and then Li ions. However, it does not occur continuously because while the doping concentration approaches a given critical value (0.65 mol % into the crystal), the Li concentration reaches a maximum, and the Li vacancies and niobium antisites remain practically constant. At this critical doping concentration point, the crystal stops the introduction of indium into its structure. After this critical value, as the doping concentration increases, the In replaces the Li but also the Li vacancies and niobium antisites. The niobium antisite is not the most stable point defect due to as the In-doping increases it takes values between five and fourteen times lower than the Li vacancies. From a compressive strain in the lattice of LN crystals induced by the In ion, the phonon modes with a Raman shift in the range from 300 to 500 cm−1 were appreciably attenuated. Close to the peaks centered at 151 cm−1 and 878 cm−1 appeared one extra vibration mode for crystals doped with 2.0 mol % and 1.3% mol of In in the melt, which reveals important structural changes induced by the In ion.