AC susceptibility and electrical properties of Cr and Mo substituted Tl(BaSr)CaCu2O7 Tl-1212 type phase superconductors

The Ba and Sr bearing Tl(BaSr)CaCu 2 O 7 (Tl-1212) phase is an interesting superconductor. Optimizing the average copper valence can lead to a high transition temperature, T c . Single elemental substitution can be used to optimize the Cu valence. This work investigated the effects of multivalent Cr and Mo substitutions at the Tl site of Tl 1- x M x (BaSr)CaCu 2 O 7 (M = Cr and Mo). The samples were prepared via the solid-state reaction method. The structure and lattice parameters were determined using the X-ray diffraction method (XRD). A field emission scanning electron microscope (FESEM) was utilized to observe the microstructure. The electrical resistance and AC susceptibility were measured to determine the transition temperature. XRD pattern showed a single Tl(BaSr)CaCu 2 O 7 phase for the non-substituted sample. Other phases, such as Tl-1201 and Ca 0.3 Sr 0.7 CuO 2 were also observed in the Cr and Mo substituted samples. The non-substituted sample showed onset transition temperature, T c-onset of 108 K. The highest T c-onset was observed in the Tl 0.9 Mo 0.1 (BaSr)CaCu 2 O 7 (115 K) and Tl 0.5 Cr 0.5 (BaSr)CaCu 2 O 7 (111 K) samples. The intergranular critical current density was between 17 and 22 A cm −2 . Cr substitutions for x = 0.1 to 0.5 and Mo substitutions for x = 0.1 showed the highest transition temperature. These results can be used as guides to improve the superconducting properties of the Tl-1212 phase.