Superconductivity in (Tl0.5Pb0.5)(Sr2.8-xCaxPr0.2)Cu2O7-z

초록

Polycrystalline samples of (Tl<inf>0.5</inf>Pb<inf>0.5</inf>)(Sr<inf>2.8-x</inf>Ca<inf>x</inf>Pr<inf>0.2</inf>)Cu<inf>2</inf>O<inf>7-z</inf> with 0 ≤ × ≤ 2.3 were synthesized by using a solid-state reaction method. The structure and the physical properties were investigated by means of X-ray diffraction and transport measurements. We observed that the 1212 phase was mainly formed for compositions with values of × above 0.4 and that nearly single-phased samples were obtained for samples with 0.6 ≤ × ≤ 1.0. The maximum zero T<inf>c</inf> of 100.8 K was observed for the Ca-doped sample with x = 0.8. Contrary to the expectation for homovalent substitution, the value of T<inf>c</inf> decreased as the Ca-doping content was increased above x = 0.8. The superconducting behaviors induced by Ca doping are discussed in conjunction with the change in the hole concentration estimated from the thermoelectric power.

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