1. Pietrokowsky, P., thesis, Calif. Inst. Tech. (1959).
2. Johansson, C. H., and Linde, J. O., Ann. Physik, 78, 439 (1925).
3. Humble, S. G., Acta Cryst., 17, 1485 (1964).
4. Pietrokowsky, P., J. Inst. Metals, 90, 434 (1961).
5. Raub, E., Walter, P., and Engel, M., Z. Metallkunde, 43, 112 (1952).