Synthesis and characterization of (Tl1-xMx)(Ba,Sr)(2)Ca2Cu3Oz (M = Pb, K, Bi) cuprates: The chemical control of high-temperature superconductivity

Abstract

The correlation of dopant stoichiometry and superconducting transition temperature (T-c) of three series of metal-doped (Tl1-xMx)(Ba-0.5,Sr-1.5)Ca2Cu3Oz (M = Pb, K, Bi; M-doped Tl-1223) cuprates was investigated. X-ray pure samples were obtained for all phases with x less than or equal to 0.25, less than or equal to 0.25 and 0.60 for M = K, Bi and Pb, respectively. The T-c's of M-doped Tl-1223 phases were found to increase significantly with increasing M content for M = Pb and Bi, whereas that for M = K tends to decrease slightly, as indicated by Meissner effect measurements. The enhancement or suppression of superconductivity (i.e., T-c of Tl-223 upon M-doping can not be satisfactorily rationalized without including both empirical oxygen and TI stoichiometry as well as M content.