Anisotropic thermal parameters of Nb in Nb3Sn

Results of the first complete measurements of Bragg reflections for a single crystal of Nb3Sn with a superconducting transition temp. Tc, of 18.2 deg K were obtained. A high anisotropy in the vibrations of the atoms along and across the chains of the transition metal suggests a covalent character for the chemical bond between the atoms. Nb3Sn had the max. anisotropy among the superconducting single of various A15 compounds studied. A correlation between Tc and the degree of anisotropy of the thermal vibrations of the transition-metal atoms was found. 7 ref.--BA