Crystal structure and physical properties of layered Na[formula omitted]Fe[formula omitted]S[formula omitted]O.

Layered iron oxysulfide Na 2 Fe 2 S 2 O 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. Na 2 Fe 2 S 2 O crystallizes in an anti-K 2 Ni F 4 -type structure, which gives rise to the characteristic [Fe 2 S 2 O] 2 − block layers. The physical property measurements indicate that it is an antiferromagnetic insulator with a Néel temperature of T N = 91. 5 K and an energy gap no less than 0.43 eV. Evidence of two-dimensional short-range spin correlations above T N is given by the magnetic and specific-heat measurements. Our structural correlation analysis suggests that the Fe–S bond distance dominantly determines T N. [Display omitted] • High-quality samples of Na 2 Fe 2 S 2 O were prepared by an optimized synthesis condition. • The crystal structure was precisely determined by powder X-ray diffraction. • The title material is demonstrated as an antiferromagnetic insulator. [ABSTRACT FROM AUTHOR]