Ceramic Tl-oxide based superconductors reinvestigated by magnetic separation technique and SQUID measurements

Ceramic samples of Tl2Ba2Ca2Cu3O10 (Tl-2223) and TlBa2Ca2Cu3O9 (Tl-1223) superconductor were resynthesized by using several preparation procedures and investigated by means of magnetic separation technique, allowing evaluation of the superconducting critical temperature of individual grains as small as 25 μm. Although an onset of diamagnetism detected by SQUID measurements was observed around 130 K in Tl-2223 and 134 K in Tl-1223, no grains with Tc > 125 K were found for Tl-2223 and with Tc > 130 K for Tl-1223. Furthermore, the volume fraction of superconductivity of such ceramics was less than 5% and 3% in best samples of Tl-2223 and Tl-1223, respectively. Here we provide a detailed comparison of results obtained by magnetic separation technique with those by SQUID applied to individual grains and bulk samples.

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► Magnetic separation technique for the investigation of ceramic powder samples.
► Reinvestigation of Tl-oxide-cuprate superconductors.
► Investigation of onset of diamagnetism by a scaling method.
► Comparison of single grain diamagnetism measured by SQUID and magnetic separation.