Synchrotron X-ray powder diffraction studies on the phase transitions in LiMn2O4

Structural phase transitions of the spinel lithium-manganese oxide, LiMn2O4 (Fd3m at room temperature) in the temperature range of 300-20 K, were investigated using synchrotron and laboratory X-ray powder diffraction. Splitting of the spinel X-ray lines 311, 400, 440, 531, 533 and 622, recorded during the test, evidenced the reversible formation of cubic, orthorhombic and tetragonal structures. The first transformation starts at similar to290 K as a cubic (Fd3m) --> orthorhombic (Fddd) symmetry reduction, and both phases coexist down to 260 K. Below 100 K a second structural transition, orthorhombic --> tetragonal (F4(1)/ddm) was observed, with the coexistence of these two phases down to similar to40 K. The supercell corresponding to 3a x 3a x a (a, spinel unit-cell constant) has been considered for both orthorhombic and tetragonal polymorphs of LiMn2O4, based on the appearance of (2.10.0) superstructure X-ray reflection. (C) 2003 Elsevier B.V. All rights reserved.