JOURNAL OF THE AMERICAN CERAMIC SOCIETY, vol. 83, no. 4, page. 787 - 791, 2000-04
JOURNAL OF NON-CRYSTALLINE SOLIDS, vol. 208, no. 1-2, page. 29 - 35, 1996-11
JOURNAL OF NON-CRYSTALLINE SOLIDS, vol. 196, page. 162 - 167, 1996-03