Influence of the Off Stoichiometric Precursor to the Formation of the YBCO Superconductor Phase and Influence of Ca Doping to the Crystal Structure of YBCO Superconductor

Influence of the off stoichiometric precursor to the formation of the YBCO superconductor phase and influence of Ca doping to the crystal structure of YBCO superconductor have been investigated. In this research it were synthesized four type of YBCO samples with solid state reaction method from the powdered raw material of Y2O3, BaCO3, CaCO3 and CuO. The fourth type of samples were Y1.80Ba2.40Cu3.400O7-x, (Y0.95Ca0.05)Ba1.595Cu2.405O7-x, (Y0.80Ca0.20)Ba2.000Cu3.000O7-x, and YBa2Cu3O7-x. The samples were calcinated at Tκ = 900 oC for 5 hours, then characterized with x-ray diffraction technique. The resulted YBCO powders were pressed into pellet, then sintered at Ts = 940 oC for 10 hours. The resulted samples were characterized with x-ray diffraction technique, and Meissner effect. The x-ray diffraction data's were analyzed with the Rietveld method. The result of analysis indicate that the 123 phase and 211 phase were easier formed if it was used the off stoichiometric YBCO precursor. But if the stoichiometric YBCO precursor was used, the 123 phases was just formed perfectly after sintering process and with no second phase of 211 phase. Doping of the off stoichiometric YBCO precursor with 0.05 mole of Ca lead to substitution of some Y atoms with Ca within 123 phase crystal structure, and there is no phase transition. But when the precursor was doped with 0.2 mole of Ca, the 123 phase structure change from orthorombic to tetragonal. With precursor of (Y0.95Ca0.05)Ba1.595Cu2.405O7-x, the 123 phase and 211 phase can be grown having the ratio close to the ideal composition of (75 : 25 %), and shortest Cu(2)-O(3) chain in its 123 phase. It was confirmed that Meissner effect of YBCO superconductor sensitive to the mole amount of O atom, but it was not sensitive to the mole amount of Y, Ba, and Cu metal atoms. (author)