Effect of Cr substitution on the structure and the superconductivity in (Tl0.5Pb0.5)Sr2CuO5+z

초록

Samples with a nominal composition (Tl<inf>0.5</inf>Pb<inf>0.5-x</inf>Cr<inf>x</inf>)Sr<inf>2</inf>CuO<inf>5+z</inf> with x = 0, 0.25 and 0.5 were prepared by using a two-step solid-state reaction method and were studied by using powder X-ray diffraction (XRD), resistivity, and room-temperature thermoelectric power measurements. The XRD data revealed that all reported samples contained an almost single 1212 phase, although the phase purity of the samples degraded slightly as the Cr content was increased. The samples crystallized in a tetragonal unit cell, and the lattice parameter a increased with increasing x whereas the lattice parameter c decreased. The resistivity data showed that Cr substitution caused an increase in the superconducting transition temperature of the sample. Using the thermoelectric power as a guide, we found that Cr substitution, rather than Pb substitution, at Tl sites was more effective in decreasing the hole concentration of the sample.

키워드