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[摘要]：Two new oxyselenide materials have been synthesized with composition La2O2MSe2(M = Mn, Fe). They adopt a new structure type, the structure, which has been solved and refined from powder X-ray and neutron diffraction data. The structure is described by Ama2 symmetry with unit cell similar to 17.5 angstrom x 16.6 angstrom x 4.0 angstrom and consists of sheets of MSen polyhedra separated by La2O2Se blocks. A structural phase transition occurs on cooling involving ordering of M cations and a symmetry reduction to a primitive structure of Pna2(1) symmetry. Both manganese and iron analogues are antiferromagnetic at low temperature. beta-La2O2FeSe2 is a semiconductor in the temperature of 150-300 K with a band gap of approximately 0.7 eV while beta-La2O2MnSe2 is insulating at room temperature with band gap of 1.6 eV. |
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