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Effects of the substitution of divalent A (Ca, Sr or Ba) ion in Ce excess non-superconducting Nd1.82Ce0.18CuO4.09 compound, leading to revival of superconductivity, are studied by measuring absorption edges of all the cations with synchrotron radiation. It is found that in these NACCO samples, Cu exists mainly in the 2+ state; the weak pre-edge feature near the Cu+ position is marginally affected due to A(2+) ions. Except for the case of Pa doping, a fall in the intensity of the white line at the Cu K-edge is observed. This is attributed to a decrease in lattice oxygen content (oxygen vacancy creation) leading to an increase in electron carriers. It is noted that when the effective charge on Cu is less than or equal to 1.88, the T'-type samples are superconducting.

The oxygen vacancy parameter, delta, in electron-doped superconducting Nd1.85Ce0.15CuO4-delta, has been varied by changing the sample-processing conditions. A T(c)-onset value of 19 K was obtained by quenching alone. T(c) onset as high as 24 K, T(c)(R = 0) = 17 K and DELTAT(90%-10%) = 3 K have been achieved for delta = 0.05 in argon-annealed single-phase Nd1.85Ce0.15CuO4-delta samples.