Effects of thallium fluoride and yttrium on structure, electrical properties and ac losses susceptibility of (Bi,Pb)-2234 superconductors

We have studied the effects of thallium fluoride TlF3 and yttrium Y3+ on phase formation and superconducting transport properties of Bi1.8_xTlxPb0.35Sr2Ca3_ zYzCu4O12+delta F3x superconductors. The samples are characterized by X-ray diffraction, SEM photographs, resistivity and AC susceptibility chi '(chi '') measurements. The study showed that the melting point of the sample doped with thallium fluorine and yttrium as well as the formation temperature is decreased. We have found that the agreement factors of structure (Rp,Rwp,GOF) and the superconducting parameters as the transition width, the activation energy, the residual and normal resistivity were enhanced with TlF3 and Y3+ doping. This behavior attests of the improvement of flux pinning strength into the grains and their coupling matrix. The inter-granular AC loss peak temperature was observed to increase as doping which is mainly due to a strong links between the grains. However, it is widely decreased with magnetic field. The maximum of susceptibility (chi''max) and partial susceptibility of matrix (chi ''m,max), and the effective volume fraction of the grains (fg) are determined on the basis of the critical state model which proved a great improvement with doping under applied field of 2 and 10 Oe. The estimated values of matrix susceptibility through this model revealed the well decrease of the inter-granular losses with doping as well.