Evolution of morphological, crystal structure, and electrical properties of Ba-Pb-Bi-O superconducting materials

Bismuthate superconductor material has a transition from a semiconductor/conductor to a superconductor. Research on this transition temperature has attracted many researchers' attention to reveal this material's superconducting properties. We synthesized the materials by the solid-state reaction method. Samples were synthesized with variations in sintering temperature and also with variations in Bi-doping. X-ray diffractometer (XRD), scanning electron microscope (SEM), and resistivity versus temperature measurements were used to analyse the crystal structure, morphology, and electrical characteristics, respectively. Based on SEM results, there were no significant changes with the increase in sintering temperature. However, from x = 0 to 0.40 there was a change in the crystallization properties which changed according to the amount of doping of the Bi element. Based on the XRD results, the major phases were Ba₄Bi(PbO₄)₃ with a tetragonal crystal structure and P4/mmm space group, and BaPbO₃ with a cubic crystal structure and Pm-3m space group. The increase in the sintering temperature causes a change in the insulator-metal-insulator properties. In the variation of Bi composition, the evolution of phase formation of Ba₄Bi(PbO₄)₃ starts at x = 0.20 and then decreases drastically when x = 0.40. T_C was detected at a value of x less than 0.35, indicating that the effect of Bi composition below x = 0.35 does not significantly affect the electrical properties. The increase in the Bi composition causes changes in the metal-insulator-metal properties. At x = 0.2 to 0.25, there is a change in the crystal structure which is thought to cause the semiconductor properties to be above the T_C.