Relation of structure and superconductivity in self-compensated Y _1-xCa _xBa ₂Cu _3-xAl _xO _z system

The co-doped compounds of Y _1-xCa _xBa ₂Cu _3-x Al _xO _z, with x from 0.1 to 0.4, were synthesized through a solid-state reaction method. Structural and superconducting properties have been investigated by X-ray diffraction, Rietveld refinement, and DC magnetization measurement. The lattice constant a decreases while b increases with the addition of x. The difference between a and b diminishes gradually. Careful study of the crystalline structure shows that the critical temperature (T _c) changes monotonically with some local structural parameters, such as the difference between Ba and Cu(2) atoms' Z coordinates, the bond length of Cu(2)-O(4), and the bond angle of Cu(2)-O(2)-Cu(2), which are all closely related to the interaction between the perovskite block and the rock salt block in the unit cell. The results indicated that the influence of the crystalline structure on superconductivity is important and independent of the carrier concentration.