Influence of Tin doping on the Sm123 superconducting ceramics

Abstract

We produced the samples that consist of the nominal composition as Sm1.46Ba1.54−xSnxCu3.2Oy (x = 0.35; 0.55; 0.75 and 0.95) by the melt growth method. We investigated Sn-dopant effects regarding differential scanning calorimetry, scanning electron microscope, X-ray powder diffraction and levitation force. The X-ray powder diffraction diagrams show many Sm211 phases in the Sn-doped samples. The lattice structures belong to the orthorhombic and tetragonal unit cells for the Sn-free and Sn-doped samples, respectively. We achieved the reduction of the grain size and the percentage of the orthorhombic phase with Sn doping. The SEM images of Sn-doped samples reveal to the reduction of the grain size. The reason of phase transformation is suspected to be related to the evolution of the c-lattice parameter. It is well-known that oxygen content also causes the phase transformation of the RE123. The a, b, and c-lattice parameters correspond to the unit cell closely matched to the well-known Sm123 values in the literature. The orthorhombic (123) phase in the matrix increases later, even if it makes smaller initially in terms of grain size. In this study, the reduction of the grain size confirms the increasing of tetragonal (211) phase in the matrix. This indicates that the (211) phase has been filtered in the matrix. Namely, the Sn-dopant effect induces the increase of Sm211 phase, in this way the phase transformation occurs in the matrix.