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.