Effect of atomic doping on electronic properties transport critical current and superconductivity in bulk high Tc cuprates

By studying the effect of co-substitution on electronic properties and superconductivity it is found that a kind of substitution, provided it does not disturb the Cu-O planes directly, tends to be largely compensated by another kind of substitution which has the opposite action of that of the former. However, such compensation effect has not been observed in the case where the dopants are directly introduced to the Cu-O planes. The origins of these effects are discussed based on the measurements of electronic transport properties including the resistivity, Hall effect and electrical thermopower, lattice parameters, oxygen content and XPS. A technique based on the zone melting growth and compensation effect is developed to prepare high quality textured polycrystalline samples. Compared with the ordinary ones, samples prepared with this new method have less cracks and larger potential for carrying transport current. In addition, some characteristics of granular superconductivity, such as two peaks transition, superconductive glassy behaviour, weak link effects and etc. are also investigated in the textured and untextured samples which provide various grain boundaries and weak link states. In this paper the effects of dopant on the properties mentioned above are discussed