Magnetic Properties of YBCO-PST Composites

The magnetic properties of granular superconductor-insulator composites were investigated. The composites were random composition of the YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ (YBCO) high-temperature superconductor and Pb(Sc$\text{}_{0.5}$Ta$\text{}_{0.5}$)O$\text{}_{3}$ (PST) ferroelectric insulator. The composites exhibited lower superconducting volume ratio than the YBCO content. For samples with YBCO content low enough no global (the whole sample) and local (separated grains) superconductivity was observed. The observed decay of the superconductivity, lowering of the critical temperature, and the increase in number of paramagnetic centres as PST content increases are explained assuming reaction among YBCO and PST phases and possible formation of an additional ones, which did not exist in the initial powders.