Electrical conductivity of disordered (Bi,Pb)-Sr-Ca-Cu-O materials

Electrical properties of (Bi,Pb)4Sr3Ca3Cu4Ox material obtained by the solid state crystallization method were studied. Depending on the temperature and time of crystallization, the material is either a granular system of small oval granules of the (Bi,Pb)2Sr2CuOx and (Bi,Pb)2Sr2CaCu2Ox phases embedded in the insulating matrix or a disordered metal composed of larger crystallites weakly connected one with another. The granular materials, which below the transition temperature contain the granules in the superconducting state, have two types of temperature dependence of resistivity. These composed of very small granules (10 nm) of the superconducting phase have characteristic for the strong localization regime exponential dependence. When the granules of the 2212 phase are of about 30 nm, the bulk superconducting state is achieved. The onset of the superconducting transition is consistent with the relation between the Josephson coupling energy and Coulomb charging energy. The (Bi,Pb)-Sr-Ca-Cu-O materials crystallized for longer times are strongly disordered metals with short mean free path. The samples with ρ(T) linear and close to linear were analysed within the Mooij phenomenological model.