Intralattice Strain Analysis in Superconducting Crystals and Superconducting Electrons

The bonding distances between atoms in five different structure types of superconductors, Nb₃Sn, (La, Sr)₂CuO₄, YBa₂Cu₃O_7–δ, Bi₂Sr₂CaCu₂O_x and Tl₂Ca₂Ba₂Cu₃O_8+x were calculated. There are many shrunken bonds in all the five compounds. T_c increases with the decrease in atomic distance of cations, rather than that of Cu–O. Structures which have large rhombicity tends to have higher density without the application of ultra‐high pressure owing to the existence of a large number of oxygen; that is, the more the number of oxygen anions surrounding the cations increases, the more the radii of cations shrink. In shrunken atoms, electron orbits are forced to condense toward to the nucleus, it is considered that superconducting electrons are apparently created and perfect diamagnetism is derived from inner filled bands.