Synthesis and magnetic properties of zirconium oxide or magnesium oxide-containing yttrium barium copper oxide and bismuth strontium calcium copper oxide superconductors prepared by self-propagating chemical decompositio

Successful applications of high-T$rmsb c$ oxide superconductors require a J$rmsb c$ in excess of 10$sp5$ A/cm$sp2$ at 77 K in a strong magnetic field. There are two main reasons which decrease J$rmsb c$ significantly in the bulk, polycrystalline superconductor. One is weak-links at the grain boundaries and the other is the flux line movement within the grains due to insufficient flux pinning in the superconductor. To overcome these problems, a new improved synthetic technique is necessary to prepare the most desirable superconducting powder. The flux pinning enhancement is also required to increase J$rmsb c$ in the superconductor. In this research, self-propagating chemical decomposition method was introduced for the synthesis of YBCO and BSCCO powders. Moreover, relatively small amounts of MgO or ZrO$sb2$ were added to the initial starting compositions in an effort to provide effective flux pinning sites for improving J$rmsb c$ of these superconductors. Detailed thermoanalytical measurements were conducted to study the thermal behavior during the decomposition of the spray-dried precursors. High-temperature XRD, SEM and SQUID magnetometer were used in order to phase developments and magnetic properties of the superconductors. In the YBCO system, the precursors with 6 to 7 for the acetate to nitrate salts showed a single sharp decomposition around 270$spcirc$C. The addition of MgO resulted in the suppression of T$rmsb c$ about 80 K and the reduced J$rmsb c$ compared with undoped YBCO. YBCOs with BaZrO$sb3,$ however, showed slightly increased T$rmsb c$ and one order higher J$rmsb c$ values. In the BSCCO system, 1:5(glycine:nitrate) and 1:2($beta$-alanine:nitrate) showed a sharp exothermic decomposition below 200$spcirc$C. T$rmsb c$s of BSCCOs were decreased when the concentration of MgO or ZrO$sb2$ was increased. Small amount of MgO in BSCCO promoted the growth of 2223 phase. J$rmsb c$ of the BSCCOs with 1 and 2 vol% ZrO$sb2$ showed higher than those of undoped BSCCO at 5.5 K and 40 K. The extremely small defects induced by the substitutions or/and the formation of the other phases due to the additions are believed to be the flux pinning sites giving rise to the increased J$rmsb c$ in YBCO and BSCCO superconductors.