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In continuation of our earlier report on the EXAFS studies, we present here the results of K XANES measurements on the 3d dopants, Mn to Ni and Zn, in the 1-2-3 lattice. It is found, perhaps for the first time, that the Mn dopant in a 1-2-3 lattice is in a divalent state. It is inferred from the K XANES features that Mn occupies the Cu(1) chain site in the 1-2-3 lattice. The results of our consolidated K XANES measurements on the valence states of Fe, Co, Ni and Zn dopants are consistent with the earlier reports on these heavy 3d ions in 1-2-3 compounds.

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.