1. 57Arg: B. B. Argent and R. E. Goosey, Dept. of Metallurgy, University of Sheffield, private communication (1957) cited in [59Mil].
2. 59Mil: G. L. Miller, Tantalum and Niobium, Butterworths, London, p 566 (1959).
3. 61Pop: I. A. Popov and N. V. Shiryaeva, Zh. Neorg. Khim, 6(10), p 2334–2340 (1961) in Russian; translated as Russ. J. Inorg. Chem., 6(10), p 1184–1187 (1961).
4. 62Sav: E. M. Savitskii and U. K. Duisemaliev, Vestn. Akad. Nauk Kaz. SSR, 18, p 55–60 (1962) in Russian.
5. 63Kie: R. Kieffer, St. Windisch and H. Nowotny, Metall., 17, p 669–677 (1963) in German.