JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 15, No.3 - 4, March – April 2013, p. 229 - 234 Influence of lithium-holmium co-doped on structural and electrical properties of BSCCO superconductor G. AKÇA * , A. EKİCİBİL, K. KIYMAÇ Department of Physics, Faculty of Sciences and Letters, Cukurova University, 01330 Adana, Turkey Bi 2 Pb 0.5 Sr 2 Ca 4 Cu 6 Li x Ho x O y (0.0≤x≤0.5) samples were prepared by doping with Li and Ho at changing ratios and using melt- quenching method. Thus, the influences of different doping levels of Li and Ho on the structural and electrical properties of the BPSCCO compound have been investigated by electrical resistivity, Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (EDX) techniques. It has been observed that, with increasing Li and Ho doping, the high-T c Bi-(2223) phase gradually transforms into the low-T c Bi-(2212) and Bi-(2201) phases. However, It should be pointed out that these low-T c superconducting phases are formed at all the doping levels, but increasing amount with increasing concentration of Li and Ho. Therefore, while the electrical resistivities in the normal states increase, the superconducting transition temperatures, T c , hole concentrations, p, and the magnitudes of thermoelectric powers of all the samples decrease with increasing Li and Ho concentration x. As a result, the results suggest that with the increase in Li and Ho amount the superconductivities of all the samples are suppressed due to the destruction of the phase coherence by pair-breaking effects, or, to the hole filling mechanism with increasing x. (Received July 25, 2012; accepted April 11, 2013) Keywords: Bi-based superconductors, Li-Ho doping, DTA, Resistivity, XRD, SEM, TEP 1. Introduction The effect of substitution, of some different ions other than the main matrix ions, on the transition temperature T c of high temperature superconductors have been classified into several types by Eisaki et al. [1]. They showed that the substitution to the site location next to the apical oxygen, let us call A, especially has an influence on T c . One of the systems where foreign element can be substituted to the A site is Bi 2 Sr 2 Ca 1-x RE x Cu 2 O y . In this system, T c depends strongly on the RE element even if the ratio of Sr 2+ to RE 3+ were kept constant [1, 2]. This suggest than the site A acts not simply as a carrier reservoir but also plays a more important role in the occurrence of superconductivity. Eisaki et al. argued that the suppression of T c of Bi 2 Sr 1.6 RE 0.4 CuO y when RE is replaced by an element with a smaller ionic radius is due to a local disorder introduced by the substitution [1, 3]. In that case, the whole phase diagram may be affected by the disorder [4]. As pointed out above an interesting research area of superconductivity receiving a great deal of attention is the substitutional studies. In this content, there have been several reports on microstructural, electrical and physical properties of BPSCCO superconducting systems too [5-11]. Many workers have observed that the substitution acts as a probe of the chemical and structural environment which determines whether or not the system exhibits superconductivity [12]. These studies explain the decrease in T c for same doping materials with increasing substitutional concentration, and the subsequent metal- insulator cross over, due to the decrease in the average valance of the copper, brought about by the excess charges induced by doped ions, e.g. rare earth ions. It is known that Pb substitution at the Bi site in Bi-(2212) significantly reduces the electromagnetic anisotropy [13]. Also, the Pb substituted (2212) has shown enhanced J c in applied fields, compared to Pb free Bi-(2212) [14]. In a recent work, it is found that when RE ions are substituted in place of Sr in (Bi, Pb)-(2212), the flaky nature and the texture of the grains gradually deteriorate with an increase in RE concentration [15]. However, It is expected that there is a great scope for a further improvement of T c if the deterioration of the microstructure of the RE and Pb substituted Bi-(2212) could be suppressed. In order to explore the effects of the doping on the physical and electrical properties of the BPSCCO system extensive studies have been done by using different doping elements [9, 16-18]. The properties of BPSCCO can be governed by the doping or intercalation of the elements having a different ionic radii. Alkaline metals could be the candidate for the doping, since their ionic radii include those of Pb, Bi, Sr and Ca [19]. The effects of the alkaline metal doping in BPSCCO system were studied by Sykorova et al. and Kawai et al. [19, 20]. In their works, the T c was found to increase by Li and Na doping, but to decrease by K and Rb doping. It was also found that the alkaline metals drastically decrease the formation temperature of the Bi-(2212) phase [11]. Thus, it might be interesting to investigate the effects of co-doping of the alkaline metals and RE elements on the properties of the BPSCCO system. The study is attractive especially from the viewpoint of changing carrier concentrations. In this work, therefore, we synthesized the compounds, Bi 2 Pb 0.5 Sr 2 Ca 4 Cu 6 Li x Ho x O y (0.0≤x≤0.5), by using the well known melt-quenching method and studied the effects of co-doping of Li and Ho on the