STRUCTURE AND SUPERCONDUCTIVITY OF THE INFINITE-LAYER COMPOUND (CA1-YSRY)1-XCUO2-Z

Microstructure and superconducting properties of the infinite-layer compound Al-xCuO2-z (A=Ca1-ySry) have been investigated by high-resolution electron microscopy as well as magnetization and resistivity measurements. The alkaline earth deficient samples always contain defect-layers inserted almost randomly into the parent simple structure, where we suggest that the A cation vacancies are concentrated. High-resolution electron microscopy observations reveal that oxygen deficiency can simultaneously occur within the central CuO2 sheet of the defect layer for the sake of charge compensation for the A deficiency. p-type superconductivity with a maximum T(c) of 110 K is realized if the oxygen defects are filled in by application of high oxygen pressure on high-pressure synthesis (z approximately 0). On the other hand, n-type superconductivity also occurs in the same structure when oxygen deficiency is increased so that z > x by a heat-treatment in a reducing atmosphere under high pressure. The fundamental relationship between structure and superconductivity is discussed on the basis of the demonstrated structural uniqueness of the title compound.