Synthesis, Structure and Properties of Several New Oxychalcogenide Materials with the General Formula A₂O₂M₂OSe₂ (A = La−Sm, M = Fe, Mn)

We report the synthesis of a series of manganese-containing oxychalcogenides with general formula A 2 O 2 Mn 2 OSe 2 ( A = La, Ce, Pr) as well several new A 2 O 2 Fe 2 OSe 2 materials ( A = La−Sm). We report the structural, magnetic, and conduction properties of the manganese-containing materials: La 2 O 2 Mn 2 OSe 2, Ce 2 O 2 Mn 2 OSe 2, and Pr 2 O 2 Mn 2 OSe 2 . These materials are isostructural with La 2 O 2 Fe 2 OSe 2, and are shown to undergo a phase transition on cooling, apparently related to displacement of oxide ions from the [Mn 2 O] 2+ plane. Peak splitting has been observed in the Pr 3+ containing material at low temperatures, consistent with a reduction to orthorhombic symmetry. All of the manganese containing materials order antiferromagnetically on cooling with k = (0, 0, 0), T N = 164−184 K, and have a 12 K Mn 2+ moment of around 4 μ B . The magnetic structure of La 2 O 2 Co 2 OSe 2 is also reported. Conductivity studies have shown that La 2 O 2 Mn 2 OSe 2 and La 2 O 2 Co 2 OSe 2 are both semiconducting, with activation energies of ∼0.24 and 0.35 eV.