Synthesis, structure, and magnetic properties of the layered iron oxychalcogenide Na2Fe2Se2O

A new layered iron oxychalcogenide, Na2Fe2OSe2, has been synthesized and structurally characterized by powder x-ray diffraction. The structure is formed by alternate stacking of the newly discovered [Fe2OSe2](2-) blocks and double layers of Na+. Conductivity study shows that Na2Fe2OSe2 is a semiconductor with an activation energy of 0.26 eV. Magnetic susceptibility and heat capacity measurements reveal that an antiferromagnetic phase transition occurs at T-N = 73 K. A broad maximum of magnetic susceptibility and a slow decay of the specific heat above T-N arise as a result of two-dimensional short-range spin correlation.