Effect of non-magnetic rare earth substitution for A site in mixed anion APX superconductors

Abstract

We report the improvement of superconducting transition temperature (T c) by nonmagnetic rare earth atom substitution for A site in APX-based Zr(P, S)2, Hf(P, Se)2 and Hf(P, S)2 superconductors. The partial non-magnetic rare earth Lu atom substitution at Zr site of ZrPS, as opposed to the case of Zr(P, Se)2, shows that lattice constants a and c decrease monotonically with increasing nominal substitution y. It is shown that the maximum T c for ZrPS was increased from 3.70 K to 6.36 K. In HfP1.55Se0.45, when Hf site is partially substituted with Lu atoms (or Y atoms), lattice constant a shrinks and c expands monotonically with increasing nominal rare earth substitution y. T c was also increased from 4.88 K to 5.89 K. In HfP1.45S0.55, when Hf site is partially substituted with Lu atoms (or Y atoms), lattice constant a shrinks slightly and c expands monotonically with increasing y. T c was also increased from 3.16 K to 5.86 K. In this paper, the doping behaviour by partial substitution and the increase of T c is discussed.