Effect of acids on crystallization of lithium borate films

Abstract

Lithium borate films in amorphous and crystalline(Li2B4O7)states were prepared from alkoxide solutions hydrolyzed in thepresence or absence of hydrochloric acid or acetic acid. The acidssuppressed crystallization of the amorphous films intoLi2B4O7, with acetic acid being the stronger suppressor. Inorder to determine the suppressing mechanism, we investigated thedistribution of boron-containing species in the solutions by 11B-NMR. Boron in the non-acidified solution existed as bothB(OH) $$_4^ - $$ and polyborate species, includingB4O5(OH) $$_4^{2 - } $$ , which is easilytransformed into the crystalnucleous of Li2B4O7. In the solutionscontaininghydrochloric acid or acetic acid, however, boron was present mainlyas B(OH)3 and the formation of the polyborate species wassuppressed, leading in turn to the suppression of crystallizationinto Li2B4O7. X-ray fluorescence analysis showed thatacetic acid produced a larger amount of residual carbon in the filmsthan did hydrochloric acid. We concluded that the residual carbonalso inhibited crystallization of the films intoLi2B4O7.