Superconductivity in oxygen-added Zr5Pt3

Mn5Si3-type structure has been offering an interstitial chemistry. Recent report of enhancement of superconductivity in a Nb-based Mn5Si3-type compound by addition of an interstitial atom motivated us to investigate the effect of oxygen-addition in Mn5Si3-type Zr5Pt3. The superconducting critical temperature of 6.4 K in the parent Zr5Pt3 is monotonously reduced to 3.2 K in Zr5Pt3Ox (x=0.6) with increasing oxygen-content. As x is further increased from 0.6 to 2.5, exceeding the full occupancy of oxygen site (x=1.0), samples become multi-phases composed of Zr5Pt3O0.5-0.6, ZrPt and ZrO2. However, the superconducting critical temperature slightly increases to 4.8 K at x=2.5. The metallographic observation has revealed a change of microstructure at x>=1.0. The change of microstructure and/or the composition effect would be responsible for the enhancement of superconductivity.