Flux Synthesis, Crystal Structures, and Magnetic Ordering of the Rare-Earth Chromium(II) Oxyselenides RECrSeO (RE = La-Nd).

The rare-earth chromium(II) oxyselenides RECrSeO (RE = La-Nd) were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined by single-crystal and powder X-ray diffraction (PbHgClO-type, C2/m, Z = 2). The magnetic structure of LaCrSeO was solved and refined from neutron powder diffraction data. Main building blocks are chains of edge-sharing CrSeO octahedra linked together by two edge-sharing ORECr tetrahedra forming infinite ribbons. The Jahn-Teller instability of divalent Cr (d) leads to structural phase transitions at 200 and 130 K in LaCrSeO and CeCrSeO, respectively. RECrSeO are Curie-Weiss paramagnetic above T ≈ 14-17 K. Neutron powder diffraction reveals anti-ferromagnetic ordering of the Cr moments in LaCrSeO below T = 12.7(3) K with an average ordered moment of 3.40(4) μ/Cr at 4 K, which was confirmed by muon spin rotation experiments.