The temperature dependence of the crystal structure of the ferromagnetic superconductor RuSr2(160Gd1.3Ce0.7)Cu2O10-σ, which orders magnetically at TC ∼ 180 K and exhibits a Tc ∼ 30 K, has been investigated by time-of-flight neutron powder diffraction. In this system superconductivity is believed to occur in the CuO2 layers while the magnetic order is associated with the Ru moments. The tetragonal structure evolves from that of YBa2Cu3O7-σ by inserting a fluorite-type Gd1.3Ce0.7O2 layer instead of the Y ion and replacing the chain copper site with RuO6 octahedra. Rietveld analysis reveals that the basal oxygens of the RuO6 octahedra are displaced within the xy-plane to accommodate physically reasonable Ru-O in-plane bonds. These displacements are consistent with rotations of the octahedra by ∼ 15° around the c-axis. Data were collected at 40 K, 70 K, 100 K, 130 K, 150 K, 170 K 190 K and 230 K but no large structural response associated with the ferromagnetic transition is observed. A small level of oxygen deficiency within the (Gd/Ce)2O2−x, fluorite layer (x = 0.1) is detected leading to a refined stoichiometry of RuSr2(Gd1.3Ce0.7)Cu2O9.9.

The most promising way to improve jc in superconductors is likely to be a creation of small precipitates in the material during decomposition of supersaturated solid solution. It was recognised recently that Pb-doping of 2212 could have beneficial effect on jc. Bi2.1−xPbxSr2CaCu2O8+d (x=0.1…0.7) was prepared at different temperatures and oxygen partial pressure (pO2=10−3 – 0.21 atm) via nitrate route. The effect of pO2 and Pb-doping on Bi-2212 phase formation was explored with XRD, SEM/EPMA and TEM/SAED. The limit of Pb solubility in Bi-2212 was found to increase with a decrease in pO2 and corresponded to a decrease in x=0.3 at pO2 = 0.21 atm (850 °C) and x=0.6 at pO2 ∼ 10−3 atm (750 °C). TEM study of the as-synthesized solid solutions revealed significant nanoscale inhomogeneity attributed to Pb-segregation. For the samples with x > 0.3 the inhomogeneity quite often looked like a well- ordered wave with the period of about 10 nm. The samples of (Bi,Pb)-2212 processed under pO2 conditions were oxidized at 600–750°C in air for 0.5–60 h in order to cause precipitation of secondary phases from the supersaturated solid solution. Thermogravimetrical study (TG) of the oxidation gave a strong evidence of two stages composing the process. It was found that jc was enhanced by a factor of 2 after annealing at 650°C (i.e. during the first stage of oxidation).

Using quantitative magneto-optics and an inversion scheme of Biot-Savart's law the local current carrying capability of various types of grain boundaries (GB's) and interfaces in YBaCuO thin films and bulk material was investigated. In all GB's and interfaces a spatial variation of the local critical current density jc was observed which, however, has different reasons, such as microstructural inhomogeneities, magnetic field dependence of jc and size effects in extended GB's and networks of low angle grain boundaries (LAGB's).