CONGRUENT COMPOSITION AND SOLID-SOLUTION RANGE OF LI2B4O7 CRYSTAL

Congruent melt composition for Li2B4O7 single crystal growth was inves tigated by surveying the residual melt obtained after the quick growth of Li2B4O7 polycrystals under strong stirring in the melt. Residual p roducts were examined by X-ray diffraction (XRD) and differential ther mal 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 stoichiometr ic composition, 33.334 mol% Li2O, lies. Thus, the congruent melt compo sition is very close to the stoichiometric composition for Li2B4O7 wit hin the error range of 0.2 mol% Li2O. The solid solution range of Li2B 4O7 in the Li2O-rich side is constrained to be less than 0.35 mol% Li2 O by investigating the solubility limit of Li2O into the Li2B4O7 phase .