Aging and Environmental Effects on the Superconductor [Y_1 - xCa_x]SrBaCu_2.80(BO_3)_0.20O_y with 0.10 ≤ x ≤ 0.50

The long-term (more than 20 years) aging effect and degradation study of a [Y_1 - xCa_x]SrBaCu_2.80(BO_3)_0.20O_y powder ceramic superconductors with 0.10 ≤ x ≤ 0.50 are studied by X-ray diffraction and DC Magnetic Property Measurement System (DC-MPMS-SQUID). The samples prepared by solid state reaction were well characterized and stored at normal conditions of pressure and temperature for more than 20 years. The aged samples present the formation of BaCO3 due to the exposure with the environment during that period. The temperature dependence of the magnetization under Hext = 10 Oe reveal that the superconducting state remains in the samples, except for that with x = 0.10, where a higher magnetic field (20 kOe) is required to be applied to observe a superconducting response. Remarkably, the samples show the same TC values despite the aging indicating that the magnetic alignment of the formed BaCO3 affects the magnetic propertied of the whole sample but not the superconducting alignment of the doped YBCO. This is also reflected in the χ^-1(T) plots at normal state, which show both ferromagnetic and antiferromagnetic contribution, in contrast to what was obtained in the pristine samples which only presented antiferromagnetic coupling. From M(H) loops, the critical current density values at 10 K are obtained by using the critical Bean model in order to estimate the transport capabilities of the aged powders.