Crystal Structure and Physical Properties of Layered Na2fe2s2o

Layered iron oxysulfide Na2Fe2S2O serves as a cathode material for Na-ion batteries as well as a possible parent compound of novel superconductors. Here we report the crystal structure and physical properties on the basis of our successful synthesis of the high-purity sample. Na2Fe2S2O crystallizes in an anti-K2NiF4-type structure, which gives rise to the characteristic [Fe2S2O]2- block layers. The physical property measurements indicate that it is an antiferromagnetic insulator with a Néel temperature of TN = 91.5 K and an energy gap no less than 0.43 eV. Evidence of two-dimensional short-range spin correlations above TN is given by the magnetic and specific-heat measurements. Our structural correlation analysis suggests that the Fe-S bond distance dominantly determines TN.