We have refined a simple sol-gel route to prepare superconducting YBa2Cu4O8 under one atmosphere oxygen pressure. Different substitution effects in YBa2Cu4O8 were systematically studied. The influence of replacing Cu by Mn, Fe, Co, Ni, Zn on the structural and superconducting properties of YBa2Cu4O8 was studied.
Recently we described the use of a sol-gel method for synthesizing of Sr-substituted samples, Y(Ba1-xSrx)2Cu4Oy, demonstrating that Sr substitutes preferentially in the Ba site. We found that nearly single-phase superconducting Y(Ba1-xSrx)2Cu4O8 samples were obtained where x = 0.00 0.30, while impurities as major phases appeared over x = 0.50. The Y-124 phase did not form in the sample with x ≥ 0.75. Moreover, we have demonstrated that the substitution of Sr2+ ions for Ba2+ ions in the YBa2Cu4O8 system has significant effect on the superconducting properties. With increasing Sr content Tc increases and a maximum value appears at x = 0.20 with a Tc of 88 K.
For the first time we have successfully applied the sol-gel technique to the preparation of Hg-based superconductors (HgBa2CaCu2O6+d and HgBa2Ca2Cu3O8+d), with the highest superconducting transition temperatures found so far. The synthesis of thallium-substituted mercury-based superconducting material has also been performed.