Анотація:
We adopted the x-ray diffraction, oxygen contents, positron annihilation technology as well as simulation
methods to investigate systemically YBa₂Cu₃–x(Ni,Co)xO₇–δ (x = 0–0.5). The simulated results show
that ions distribute in dispersive form in little doped concentration. As doped concentration increases, ions
combine into clusters in the crystal lattice. The calculated results and oxygen contents, together with the impure
phases and the local electron density ne, show the ionic cluster effect, which not only causes the local
electron density to reach the saturation, but also suppress the superconductivity significantly.