1. Al’Shin and Astrov, D. N...Soviet Physics, JETP, 1963,17, 809.
2. Astrov, D. N... Ibid., 1960,11, 708.
3. Bhagavantam, S...Proc. Ind. Acad. Sci., 1942,16, 359.
4. —— and Suryanarayana, D.Acta Cryst., 1949,2, 21.
5. Borovik-Romanov, A. S...Soviet Physics, JETP, 1959,9, 1390.