Influence of factors on growth of off-congruent LiNbO₃ single-crystal by li-rich/li-poor chemical vapor transport equilibration

Influence of factors on growth of off-congruent LiNbO₃ single-crystal by Li-rich/Li-poor chemical vapor transport equilibration (VTE) was studied. These factors include the molar ratio of raw materials Li ₂CO₃ and Nb₂O₅ for preparing two-phase crucible, the hollow space volume for VTE growth, and the period of use of two-phase crucible. To achieve the goal, a number of off-congruent LiNbO₃ plates were grown by Li-rich/Li-poor VTE technique using four two-phase crucibles having different molar ratios of raw materials, hollow space volumes, and periods of use. The VTE-induced crystal composition alteration was characterized by measurement of birefringence. A comparison of results of different crucibles shows that in the Li-rich VTE case the first factor has less effect, while the latter two may cause a difference of Li₂O content as much as 0.4 mol %. Larger hollow space volume and older crucible tend to degrade the VTE growth efficiency. Instead, the growth by Li-poor VTE is less affected by the three factors because of much lower Li₂O gas pressure and hence slow growth rate in comparison with that by Li-rich VTE.