IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 13, NO. 2, JUNE 2003 3155 Effect of 3d-Metal Sulfide Doping on the Superconducting Properties of Bi-2212 Superconductors C. L. S. Lima, P. B. Silva, E. Montarroyos, Y. P. Yadava, and J. Albino Aguiar Abstract—In the present work, we have studied the effect of 3d metal sulfide doping on the superconducting properties of the Bi-2212 superconductors with the nominal composition Bi Sr Ca CuO MS O , where Ni, Cu, Zn, Ti. The samples were synthesized by solid state reaction process. Structural and magnetic characterization was carried out using x-ray diffractometry and magnetic susceptibility measure- ments. All the samples exhibited stabilization of superconducting Bi-2212 phase and reduction of superconducting transition temperature . ZnS and TiS substitution for CuO planes and modification of oxygen content due to S substitution on O places jointly produce strong localization of charge carriers and at the same time improve the hole concentration of the system. These combined phenomena are responsible for the deterioration of su- perconductivity of ZnS and TiS doped Bi-2212 superconductors. Index Terms—3d metal sulfide doping, Bi Sr Ca CuO MS O , Bi-2212 superconductors, magnetic susceptibility, structure. I. INTRODUCTION S INCE the discovery of high- superconductors, the substitucional and doping studies have proved to be very useful in understanding the basic aspects of their properties. Since most of the high temperature superconductors, discov- ered till now, are cuprates, Cu atoms are of prime importance when it is supposed that superconductivity resides in the CuO planes. Among high- superconductors, BiSrCaCuO system is a simpler and better candidate for studying the effect of substitution on the superconducting properties [1], [2]. But at the same time, this system is one of the more difficult systems to have high reproducibility and find desired proprieties. Influence of many parameters: thermal treatment, amount of oxygen content, complex phase diagrams (local and global) etc. play important role in the superconducting proprieties of this system. The superconducting transition temperature can be changed by changing the number of conducting layers, doping the samples or changing carrier concentration. Normally 3d-metal oxides are used for substitution and doping studies in high ceramic superconductors. In a study on doping effects on superconducting properties of high ceramic superconductors, Aguiar et al. [3] observed that in YBa Cu O superconductors metal sulfide doping is less Manuscript received August 6, 2002. This work was supported in part by the Brazilian Agencies CAPES, CNPq and FACEPE. The authors are with the Departamento de Física da Universi- dade Federal de Pernambuco, 50670-901, Recife-PE, Brazil (e-mail: clsl@df.ufpe.br; pbs@df.ufpe.br; erimont@df.ufpe.br; yadava@npd.ufpe.br; albino@df.ufpe.br). Digital Object Identifier 10.1109/TASC.2003.812128 effective in deteriorating the superconducting transition tem- perature than metal oxide doping. Using a similar approach, in our recent studies, we have successfully achieved stabilization in superconducting properties of Bi-2212 superconductors using CuS and NiS doping and eventually, we observed a substantial increase in of Bi-2212 superconductors doped with CuS [4], [5]. Within this context, extending our studies on the effect of 3d metal sulfide doping on the superconducting properties of the Bi-2212 superconductors, in the present work, we present our results concerning the effect of TiS and ZnS doping on the superconducting properties of Bi-2212, with the nominal composition Bi Sr Ca CuO MS O , Zn Ti . II. EXPERIMENTAL DETAILS Bi Sr Ca CuO MS O , , where Zn, Ti, were prepared by solid state reaction process. Constituent chemicals Bi O , SrCO , CaCO , CuO and ZnS or TiS (purity 99.99%) were mixed in desired stoichiometric ratio and were dried at 200 C for 6 h. The dried mixture was finely powdered and pelletized as circular discs, at a pressure of 2 ton/cm . The pelletized samples were calcined at 800 C for 40 h. After calcination, samples were cooled down to 500 C at a cooling rate of 1 C/min and after that the samples were furnace cooled to room temperature. Calcined material was reground finely and pelletized at a pressure of 2 ton/cm . Final heat treatment of samples was carried out at 850 C for 100 h in air atmosphere. Samples were cooled down slowly at a rate of 1 C/min to 500 C for proper oxygenation and finally furnace cooled to room temperature. X-ray diffraction (XRD) spectra of the samples were recorded at room temperature by a Siemens D-5000 x-ray diffractometer, using CuK radiation . Superconducting properties of the samples were studied by measuring dc magnetic susceptibility in the temperature range 5 to 300 K, at an applied ac magnetic field of 0.1 Oe and frequency of 31 Hz, using a Quantum Design (MPMS–5S) SQUID magnetometer. III. RESULTS AND DISCUSSION The XRD spectra of the Bi Sr Ca CuO MS O samples are shown in Figs. 1 and 2. From an analysis of the XRD peaks of Bi Sr Ca CuO MS O samples follows the conclusion that all the samples present a typical crystal structure of Bi-2212 superconductors. In the XRD spectra of the samples, there are no reflections due to Bi-2201 and Bi-2223 superconducting phases. 1051-8223/03$17.00 © 2003 IEEE