1 Dwight, A. E., The Rare Earth in Modern Science and Technology, Proc. 13th Rare Earth Res. Conf. (1977) , Eds. Macarthy, G. J.; Rtyne, J. J., Plenum, New York, 1978, p. 325.
[2]
2 Van Mal, H. H., J. Less-Common Met., 35 (1974) , 65.
[3]
3 Shinar, J.; Shaltiel, D., J. Less-Common Met., 60 (1978) , 209.