EXTENDED X-RAY ABSORPTION FINE-STRUCTURE STUDIES OF 3D IONS IN YBA2(CU1-XMX)3O7-DELTA (X-LESS-THAN-OR-EQUAL-TO-0.10-M EQUIVALENT-TO MN, FE, CO, NI AND ZN)

EXAFS measurements on 3d ions in samples of nominal composition YBa2(Cu1-xMx)3O7-delta (x less-than-or-equal-to 0.10; M = Mn, Fe, Co, Ni and Zn) were made in fluorescence mode using the synchrotron radiation source at Daresbury Laboratory. The standard Daresbury packages including the EXCURV90 program were used to identify the dopant site occupancy and to evaluate the coordination number and bond lengths. It is found, perhaps for the first time, that the Mn2+ ion occupies the Cu(1) chain site in the 1:2:3 lattice. The occupancy of the Cu(1) site by Fe and Co dopants is confirmed. Ni ions are distributed nearly equally between Cu(1) chain and Cu(2) plane sites. For x > 0.03, some of the Ni separates out as NiO and the maximum Ni content in the 1:2:3 compound has been estimated to be 4 +/- 1 at.%. No useful data could be obtained for Zn dopant owing to interference from the adjacent Cu K edge in the 1:2:3 compound. An attempt has been made to interpret the observed drop in T(c) due to substitution on the basis of EXAFS findings.