Annealing effects in (Hg,Cr)Sr2CuO4+delta: Transport and X-ray absorption studies
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Superconducting (Hg1-xCrx)Sr(2)CuO(4+delta,)x similar to 0.36, samples of 1201-type synthesized in partial vacuum, show T-c(onset) of similar to 58 K, T-c (R = 0) similar to 52 K. It is found that T-c is not affected by the subsequent Ar or O-2 annealing treatment. Remarkably, the annealed samples show significant improvement in the diamagnetic signal. Hg L-3-edge measurements on 1201 samples show divalent state of mercury. The Cu K-edge spectra for the samples, after taking due account of the impurity phases. show noticeable modifications in the split main peak features on Ar or O-2 annealing, suggesting changes in the crystal field asymmetry. In the superconducting (SC) samples, a weak but distinct signature of Cu1+ is seen. The Cu1+ feature is absent in all the non-SC 1201 samples as well as in the impurity phase SrCuO2 and Sr2CuO3 samples. An attempt is made to explain the observed Cu1+ feature in SC (Hg,Cr)-1201 in the light of the available reports.
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