Synthesis, structure and properties of layered iron-oxychalcogenides Nd₂Fe₂Se_2−xS_xO₃

A new series of sulfur-substituted iron-oxychalcogenides Nd₂Fe₂Se_2−xS_xO₃ (0≤x≤0.4) was synthesized by solid state reaction method, and investigated by structure, transport, magnetic and specific heat measurements. The compounds crystallize in the layered tetragonal structure with I4/mmm space group, and show semiconducting behavior. The large discrepancy between the activation energies for conductivity, E_ρ (152–202 meV), and thermopower, E_S (15.6–39.8 meV), indicates the polaronic transport mechanism of the carrier. The parent compound Nd₂Fe₂Se₂O₃ exhibits a frustrated antiferromagnetic (AFM) ground state, and the S-substitution induces an enhanced ferromagnetic (FM) component and possible increased degree of frustration. - Graphical abstract: The crystal structure of Nd₂Nd₂Fe₂Se_2−xS_xO₃ is built up by stacking fluorite-like Nd₂O₂ layers and anti-CuO₂-type Fe₂O(Se/S)₂ layers with Fe²⁺ cations coordinated by two in-plane O^2- and four Se^2- above and below the square Fe₂O plane. - Highlights: • We have synthesized a new series of layered iron-oxychalcogenides Nd₂Fe₂Se_2−xS_xO₃. • They crystallize in layered tetragonal structure and show semiconducting behavior. • The transport analysis indicates the polaronic transport mechanism of the carrier. • The parent compound shows a frustrated antiferromagnetic (AFM) ground state. • The S-substitution induces an enhanced ferromagnetic (FM) component