SUPERCONDUCTIVITY IN THE CERIUM-SUBSTITUTED 2212 BISMUTH CUPRATE - BI2SR2CA1-XCEXCU2O8+DELTA

The magnetic and superconducting properties of the 2212 bismuth cuprate have been studied after partial substitution of calcium by cerium in the Bi2Sr2Ca1-xCexCu2O8 + delta(x less-than-or-equal-to 0.3) system. Synthesis conditions show that a very small cerium doping (less than 10%) is enough to increase the domain of formation of the 2212 phase by at least 30-degrees-C. Cerium is non-magnetic in these materials and does not suppress the superconducting state of the matrix. The critical temperature T(c) varies non-monotonically and reaches a maximum for x approximately 0.02, before dropping to almost zero at the limit of solubility (x approximately 0.3). Results are explained by a variation of the number of holes due to the substitution of divalent calcium by tetravalent cerium. The influence of texturation on the intragranular magnetic properties was also studied. X-ray diffraction, SEM observations, AC susceptibility and magnetization measurements clearly show that these ceramics become easily textured by their simple compaction prior to sintering. It was found that such a texturation mainly affects the intragranular properties and the initial slope of the magnetization cycles. A very slight dependence of the magnetic anisotropy as a function of the cerium concentration was noticed. Texturation is explained by simple models which take into account the size and shape of the crystallites in the decoupled regime.