PHYSICAL REVIEW B, vol. 48, no. 9, page. 6217 - 6224, 1993-09-01
MATERIALS LETTERS, vol. 12, no. 4, page. 233 - 241, 1991-11
JOURNAL OF PHYSICS-CONDENSED MATTER, vol. 5, no. 37, page. 6911 - 6924, 1993-09-13