1. 1) D. E. Maguire, International Symposium of Ta and Nb, September 1995, Goslar, Germany.
2. 2) G. J. Korinek, Bulletin of Ta-Nb Int. Study Center, No. 80, December 1994, Page 4.
3. 3) T. B. Tripp, Int. Symposium of Ta and Nb, September 1995, Goslar, Germany.