title: Spinel-to-CaFe2O4-type structural transformation in LiMn2O4 under high pressure.
abstract: A new form of LiMn2O4 is reported. The structure is the CaFe2O4-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) angstroms, b = 2.83387(18) angstroms, and c = 10.6535(7) angstroms (Pnma). Electron diffraction patterns indicated an order of superstructure 3a x b x c, which might be initiated by Li vacancies. The exact composition is estimated at Li(0.92)Mn2O4 from the structure analysis and quantity of intercalated Li. The polycrystalline CaFe2O4-type compound showed semiconducting-like characters over the studied range above 5 K. The activation energy was reduced to approximately 0.27 eV from approximately 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 approximately 10 K. As the CaFe2O4-type transition was observed for the mineral MgAl2O4, 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.
authors.affiliation: Advanced Nano Materials Laboratory, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. YAMAURA.Kazunari@nims.go.jp
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yamaura
authors.forename: Qingzhen
authors.initials: Q
authors.lastname: Huang
authors.forename: Lianqi
authors.initials: L
authors.lastname: Zhang
authors.forename: Kazunori
authors.initials: K
authors.lastname: Takada
authors.forename: Yuji
authors.initials: Y
authors.lastname: Baba
authors.forename: Takuro
authors.initials: T
authors.lastname: Nagai
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Matsui
authors.forename: Kosuke
authors.initials: K
authors.lastname: Kosuda
authors.forename: Eiji
authors.initials: E
authors.lastname: Takayama-Muromachi