Local and electronic structure of carbon and nitrogen atoms in oxycarbonitrate superconductors

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Results of X-ray fluorescence measurements of new oxycarbonitrate superconductors MSr 2Ca n−1 Cu n O y ( n=1 or 2 and M=Cu, C or N) are presented. The experiments show that C atoms form a distorted CO 3 oxyacid group with a partial substitution of copper and nitrogen atoms in the M sites. Based on the comparison of nitrogen Kα emission spectra and spectra of reference samples it is concluded that the CO 3 2− group in (C,N)Sr 2Ca n−1 Cu n O y and (Cu,C,N)Sr 2Ca n−1 Cu n O y is substituted by the NO 2 − instead of the NO 3 − group. This induces the creation of hole carriers in these compounds.