MAGNETIZATION AND MOSSBAUER STUDIES OF Y1-XCAXSR2CU3-YFEYO6+Z

ac-susceptibility, dc-magnetization, and Fe-57 Mossbauer spectra of Y1 -xCaxSr2Cu3-yFeyO6+z (x=0, 0.1, and 0.2; y=0.3 and 0.4) are presented. Our data indicate bulk superconductivity in these compounds. In the c ase of y=0.4, the substitution of x=0.1 Ca increases both T(c) and flu x pinning. The Mossbauer parameters of the sample containing y=0.4 Fe and no Ca in comparison to those of YBa2Cu3-yFeyO6+z indicate that at least 85% of Fe substitutes the Cu(1) sites and about 15% goes to Cu(2 ) sites. The existence of superconductivity at such high concentration s of Fe and the revival of superconducting properties by Ca substituti on are discussed.