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2. Berezin, A. A., Golikova, O. A., Zaitsev, V. R., Kazanin, M. M., Orlov, V. M., Tkalenko, E. N., in:Boron and Refractory Borides, (Matkovich V. I., ed.) Springer: Berlin, Heidelberg, New York 1977, p. 52.
3. Lundström, T.: see [77B1], p. 351.
4. Ipser, H., Rogl, P.: J. Less-Common Met. 82 (1981) 363.