Extensive analyses of low-temperature powder x-ray diffraction data for spinel LiMn2O4 (Fd3m at room temperature) make it clear that two structural phase transitions occur: first around 285 K from cubic to orthorhombic, second around 65 K from orthorhombic to tetragonal. At temperatures under 285 K, superlattice peaks appear in the diffraction pattern that were successfully indexed by tripling the a and b axes of the spinel unit cell. At 250 K, the unit cell is face-centered orthorhombic, Fddd, F2dd, or Fd2d, with a = 24.855(1), b = 24.755(2), c = 8.2014(3) Å, V = 5046.1(4) Å3, Dx = 4.284 g/cm3, Z = 72. The unit cell at 30 K was confirmed to be body-centered tetragonal I4 1 / amd or I4 1 /a, with a = 17.5176(3), c = 8.1961(2) Å, V = 2515.1(1) Å3, Dx = 4.298 g/cm3, Z = 36.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics