| Summary: | A new form of LiMnO is reported. The structure is the CaFeO-type and 6% denser than the spinel. The structure transformation was achieved by heating at 6 GPa. Analysis of the neutron diffraction pattern confirmed an average of the structure; the unit cell was orthorhombic at a = 8.8336(5) Å, b = 2.83387(18) Å, and c = 10.6535(7) Å (Pnma). Electron diffraction patterns indicated an order of superstructure 3a × b × c, which might be initiated by Li vacancies. The exact composition is estimated at LiMnO from the structure analysis and quantity of intercalated Li. The polycrystalline CaFeO-type compound showed semiconducting-like characters over the studied range above 5 K. The activation energy was reduced to ∼0.27 eV from ∼0.40 eV at the spinel form, suggesting a possible enhancement of hopping mobility. Magnetic and specific-heat data indicated a magnetically glassy transition at ∼10 K. As the CaFeO-type transition was observed for the mineral MgAlO, hence the new form of the lithium manganese oxide would provide valuable opportunities to study not only the magnetism of strongly correlated electrons but also the thermodynamics of the phase transition in the mantle.
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