Carbonate effects in single-crystalline YBa₂Cu₃O₇₋

Physical properties in the normal and superconducting states for CO₃ substituted YBa₂Cu₃O₇₋ single crystals are reported. From resistivity measurements in the normal state, it is obtained that the samples of the similar carrier doping, which is estimated by the c-axis resistivity, show a different behavior in the ab-plane resistivity if they have different concentrations of the carbon. The peak effects of the magnetization, which correspond to the critical current density in field, decrease with the substitution. These results suggest that the substituted carbonate affects the metallicity and superconductivity of the CuO chain layer. The substitution also suppresses the carrier doping and shortens the c-axis length as seen in polycrystalline samples. Some attention to purity of YBa₂Cu₃O₇₋ will be required because T_c can exceed 90 K for even relatively highly substituted samples, YBa₂Cu_3−x(CO₃)_0.04O_7−y. ©2010 The American Physical Society