Phase equilibria in the ternary reciprocal system Li, Ba // BO2, F and growth of bulk β‐BaB2O4 crystals

In order to find the optimum solvent for the growth of nonlinear optical β‐BaB2O4 crystals, the phase relationships in the ternary reciprocal system Li, Ba // BO2, F have been studied using solid state synthesis, differential thermal analysis and X‐ray powder diffraction. Isothermal and polythermal sections of the system Li, Ba // BO2, F are reported. In the studied system, the following compounds are formed: LiBa2B5O10 (melts by peritectic reaction at 930°C, i.e. 1203 K) and LiBaF3 (melts incongruently at 850°C, i.e. 1123 K). Visual polythermal analysis of seeding and growth of β‐BaB2O4 crystals in this system was carried out. The primary crystallization field of β‐BaB2O4 was defined. Using the top‐seeded pulling technique, a β‐BaB2O4 crystal of 93 mm in diameter, 34 mm in height and 520 g in weight has been grown. On the basis of studies using a combination of differential thermal analysis, visual polythermal analysis and solid state synthesis, a detailed investigation into phase formation in the ternary reciprocal system Li, Ba // BO2, F has been carried out and its importance in growing barium borate crystals has been shown. The liquidus of the system is composed of primary crystallization fields of six compounds – BaB2O4, BaF2, LiBaF3, LiF, LiBO2 and LiBa2B5O10 – separated by co‐crystallization curves and four nonvariant points.