EFFECT OF THE SUBSTITUTION OF BORON FOR ALUMINUM IN THE BETA-EUCRYPTITE LIALSIO4 STRUCTURE

The substitution of B for Al in the beta-eucryptite structure was examined along the compositional series described by the stoichiometry LiAl(1-x)BxSiO4 with x ranging from 0 to 1. These samples were prepared according to a sol-gel route which employs prehydrolysed tetraethylorthosilicate (TEOS), Al and Li nitrates and boric acid in aqueous solution. Two different monophasic fields were found with the beta-eucryptite and the beta-spodumene structure, respectively, with 0 less-than-or-equal-to x less-than-or-equal-to 0.40 and 0.60 less-than-or-equal-to x less-than-or-equal-to 0.80; their relative stability is discussed in terms of averaged ionic radius of B, Al and Si ions and of lithium content.