Reassembled phase diagram for Fe y Se x Te1−x superconducting films grown by pulsed laser deposition

Abstract

Fe y Se x Te targets with different Fe contents have been prepared by the solid state reaction method followed by the hot-pressed sintering, and corresponding single-phase Fe y Se x Te films with high quality have been deposited at different substrate temperatures by the pulsed laser deposition. The evolution of the structure, superconductivity and pinning mechanism of the Fe y Se x Te superconductors with the Fe content has been investigated in detail. It can be found that the excess Fe can form the residual Fe impurities scattered in the polycrystalline bulks when the Fe content in the nominal composition exceeds 1.36. More importantly, a reassembled phase diagram for Fe y Se x Te superconducting films based on the change of both Fe and Se contents is constructed for the first time. It can be clearly seen that both the Fe and Se contents can greatly affect the superconductivity of Fe y Se x Te films within a wide range of Fe content (). The Fe vacancies caused by the Fe deficiency is beneficial to the improvement of both critical temperature and activation energy, while with the increase of the Fe content, the superconductivity degrades because of the introduction of the interstitial Fe and the planar defects. The optimal Fe content at constant Se content shifts to the higher value with the increase of Se content. Our results facilitate the rational regulation of the superconducting properties, as well as the study of the underlying superconducting mechanism of FeSeTe superconductors.