Superconductivity above 50K in LnFeAsO1-y (Ln= Nd, Sm, Gd, Tb and Dy) Synthesized by High-pressure Technique

摘要

We have succeeded in synthesizing single-phase polycrystalline samples ofoxygen-deficient oxypnictide superconductors, LnFeAsO1-y (Ln: lanthanideelements) with Ln=La, Ce, Pr, Nd, Sm, Gd, Tb and Dy using high-pressuresynthesis technique. It is found out that the synthesis pressure is the mostimportant parameter for synthesizing single-phase samples, in particular forthe heavier Ln?s, such as Tb and Dy. The lattice parameters systematicallydecrease with the atomic number of Ln, reflecting the shrinkage of Ln ionicradius. For the lighter Ln?s (La, Ce, Pr, Nd), Tc increases monotonously withdecreasing the lattice parameters from 26K for Ln=La to 54K for Ln=Nd, thenstays at the constant value around 53K for the heavier counterpart (Nd, Sm, Gd,Tb and Dy). The results suggest the intimate relationship between the crystalstructural parameters and the superconductivity on the one hand, as well as thepossible existence of the inherent maximum Tc on the other, which is locatedaround 50 K in the LnFeAsO based materials.