Structure And Superconductivity Of Lifeas

摘要

Lithium iron arsenide phases with compositions close to LiFeAs exhibit superconductivity at temperatures at least as high as 16 K, demonstrating that superconducting [FeAs]~- anionic layers with the anti-PbO structure type occur in at least three different structure types and with a wide range of As-Fe-As bond angles.rnHigh temperature superconductivity has recently been reported in several compounds containing FeAs anti-PbO-type (i.e. antifluorite-type) layers. LaOFeAs with the ZrSiCuAs structure type was found to superconduct when doped with electrons through the substitution of about 10-20% of the oxide ions by fluoride. This resulted in superconductivity below about 26 K, a critical temperature, T_c, only exceeded by layered cuprate superconductors, some fullerides and MgB_2. Enhancement of T_c to 43 K was achieved in this system at high pressure. Substitution of lanthanum in LaO_(1-x)F_xFeAs by heavier and smaller lanthanides results in higher T_cs, and it has been shown that electron doping by the introduction of oxygen deficiency leads to T_cs of up to 55 K in SmO_(1-x)FeAs.