Evolution of the Structure and Magnetic Properties of the High-Tc Superconductor YBa2Cu3O6.92 in the Sol–Gel Synthesis Process

We have studied the effect of sol–gel synthesis conditions on the structural and magnetic properties of the high-Tc superconductor YBa2Cu3Oy (y = 6.92 ± 0.02). Two low-temperature (<800°C) synthesis procedures have been used, differing in the annealing sequence and atmosphere (argon or oxygen). In one procedure, the starting mixture was annealed in an oxygen atmosphere, and the resultant nonsuperconducting tetragonal phase (X-phase) was heat-treated further. In the other procedure, synthesis was carried out in an argon atmosphere, which allowed a superconducting orthorhombic phase to be obtained even after the first anneal. At the same time, it is the former synthesis procedure which has made it possible to obtain nanoparticles and prepare a series of samples with a gradually decreasing degree of structural disorder owing to sequential two-step anneals (argon + oxygen). This approach helps understand general behavior of the structural characteristics, magnetic properties, and superconducting parameters of YBa2Cu3Oy high-Tc materials differing in the degree of structural disorder.