Comparative Study of the Physical Properties of Fine-Crystalline Mechanoactivated and Sol-Gel Samples of YBa2Cu3O6.92 High-Temperature Superconductors

A technique based on the sol-gel technology is developed for the synthesis of fine-crystalline YBa2Cu3O6.92 (T-c = 91.5 K) high-temperature superconductors (HTSCs), including the step-by-step annealing of the samples in tablet form at the annealing temperature T-ann = 750 degrees C in an argon atmosphere. Having the same microstructure with the average crystallite size < D > = 200 nm, the sol-gel samples exhibit different magnetic and thermodynamic properties, depending on the number of anneals in argon. Comparison of the characteristics for sol-gel and mechanoactivated fine-crystalline samples of the same composition made it possible to make an assumption about the implementation of incomplete atomic ordering in sol-gel samples at the first stage of annealing with an increase in the degree of structural ordering during the next two stages. This may be the main reason for the change in the physical characteristics of the HTSC sol-gel samples structured at the nanoscale level, depending on the number of annealings in an argon atmosphere.