Advancement of T_c above 111 K in Li-doped trilayered Bi-2223 cuprate superconductors

Noticing the indispensable correlation between fabrication--structure--property relationship as a fundamental principle of materials physics, we performed a direct substitution monovalent Li⁺ for Cu²⁺ cations within a renovated solid-state reaction method to synthesize trilayered Bi_1.6Pb_0.4Sr₂Ca₂(Cu_xLi_1-x)₃O_10+𝛿 (x = 0--0.15) series or Li-doped Bi(Pb)-2223 compounds in observing a rare positive effect of T_c and intrinsic superconducting properties. We demonstrate that Li⁺ impurities diffuse sluggishly from a grain boundary into the high-T_c phase during the extended long-term sintering process of Bi(Pb)-2223 compounds. In addition, the presence of Li⁺ cations in the framework advances the overall copper oxidation state on the CuO₂ planes, as a result, the elevation of the hole concentration within the system enhances T_c = 111.1--113.8 K by ac magnetic susceptibility measurements compared to a standard value of 110.5--111 K. Our findings reinforce an insightful pathway to improve the critical temperature as well as intrinsic superconducting properties of the Bi(Pb)-2223 compounds by utilizing the appropriate synthesizing and doping processes.