Effect of Nb doping on the superconducting properties of (Ru,Nb,Sn)Sr2EuCu2Oz

초록

Polycrystalline samples of (Ru<inf>1-x</inf>Nb<inf>x</inf>) Sr<inf>2</inf>EuCu<inf>2</inf>O<inf>z</inf> and (Ru<inf>0.8-x</inf>Nb<inf>x</inf>Sn<inf>0.2</inf>) Sr<inf>2</inf>EuCu<inf>2</inf>O<inf>z</inf> with 0 ≤ x ≤ 0.4 were synthesized by using a solid state-state reaction method. The phase formation and the physical properties were investigated by means of X-ray diffraction and transport measurements. Contrary to the observation of no superconductivity in Sn-free Nb-doped (Ru<inf>1-x</inf>Nb<inf>x</inf>) Sr<inf>2</inf>EuCu2O<inf>z</inf> samples with x ≥ 0.2, a superconducting transition behavior was observed in the (Ru<inf>0.8-x</inf>NbxSn<inf>0.2</inf>) Sr<inf>2</inf>EuCu2O<inf>z</inf> samples, and an onset superconducting transition temperatures T<inf>c</inf>, of about 29 K and 35 K were observed for the x = 0.2 and 0.4 samples, respectively. The superconducting behaviors induced by Nb and Sn co-doping are discussed in conjunction with the changes in the hole concentration and the structure.

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