Simultaneous EDS and EELS studies on carbon in CuBa2Ca3Cu4Ox superconductors

Carbon contamination in Cu-1234 superconductors was studied using an electron-energy-loss spectroscope which was attached to a field emission electron microscope. The carbon K-edge was detected only when an electron beam of a diameter as small as 1 nm successfully incidented the charge reservoir block in a unit cell. On the other hand, the signal level of the carbon K-edge from the ‘infinite layer’ block consisting of CuO2 planes and bare Ca planes was very low. This implied that C atoms were present in the charge reservoir blocks which contained Cu. Upon annealing the sample in a reducing atmosphere of 1 atm, it was found that the high-pressure (Cu,C)-1234 phase was stable up to a temperature as high as 500°C and Tc remained constant up until phase decomposition occurred.