The influence of aluminum doping and oxygenation on the properties of YBa₂Cu₃-ₓAlₓO₆.₅+δ (0≤x≥ 0.045) HTSC

The effect of Al₂O₃ particle addition on the crystal structure and superconducting properties of YBa₂Cu₃O₆.₅+δ (YBCO) ceramics is systematically studies. Samples were synthesized using a solid reaction to prepare YBa₂Cu₃O7-δ and YBa₂Cu₃-ₓAlₓO₆.₅+δ (0≤x≥ 0.045) samples by mixing the appropriate ratios of constituent oxides; BaO, CuO, Y₂O₃ and Al₂O₃. The mixtures were ground to fine power and then calcined at 870ºC. The calcined powders were grounded again and molded into pellets by applying a hydrostatic pressure from (0.60) GPa. These pelllets were sintered at 960ºC. The structure of the prepared samples was characterized by X-ray diffraction (XRD). The crystal lattice parameters were found to change and the orthorhombicity decreased slightly with Al₂O₃ addition, and no change in the structural symmetry state was obtained. A series of YBa₂Cu₃Oy (YBCO) samples with small ammounts (0-0.45)wt.% of nanosized alumina particles (45nm) are synthesized with the flow of oxygen gas of about (1.25)L/min. The microstructure has been characterized by Scanning Electron Microscopy (SEM) and the critical temperature has been measured by the standard four-probe method in the applied magnetic filed at 77K. SEM and (XRD) analyses have shown that alumina reacts with YBCO and the superconducting transition temperature (TC) was 116 K and decreases with increasing alumina content from 108 K TO 92 K for x= 0.01 and 0.045 respectively. The iodometric titration is used to determine the oxygen content in the samples and the value of O2 varies from sample to another. The result of titration exhibited that the value of δ is increasing when increasing Al concentration.