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

Results of X-ray fluorescence measurements of new oxycarbonitrate superconductors MSr2Can−1CunOy (n=1 or 2 and M=Cu, C or N) are presented. The experiments show that C atoms form a distorted CO3 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 CO32− group in (C,N)Sr2Can−1CunOy and (Cu,C,N)Sr2Can−1CunOy is substituted by the NO2− instead of the NO3− group. This induces the creation of hole carriers in these compounds.