Congruent composition and solid solution range of Li2B4O7 crystal

Congruent melt composition for Li2B4O7 single crystal growth was investigated by surveying the residual melt obtained after the quick growth of Li2B4O7 polycrystals under strong stirring in the melt. Residual products were examined by X-ray diffraction (XRD) and differential thermal analysis (DTA) to determine if there were phases formed other than Li2B4O7, which represents the crystallization from the off-congruent melt. This ''residual melt'' method confined the congruent composition within the range of 33.232-33.537 mol% Li2O in which the stoichiometric composition, 33.334 mol% Li2O, lies. Thus, the congruent melt composition is very close to the stoichiometric composition for Li2B4O7 within the error range of 0.2 mol% Li2O. The solid solution range of Li2B4O7 in the Li2O-rich side is constrained to be less than 0.35 mol% Li2O by investigating the solubility limit of Li2O into the Li2B4O7 phase.