Synthesis and structural characterization of LiNi1/2-xMgxMn1/2O2 and LiNi1/3-xMgxCo1/3Mn1/3O2

LiNi1/2-x MgxMn1/2 O-2 (0.0 <= x <= 0.1) and LiNi1/3-xMgxCo1/3 Mn-1/3 O-2 (0.0 <= x <= 1/3) solid solutions have been synthesized and their crystal structures have been investigated. Both systems adopt alpha-NaFeO2-type layered rock-salt structure. Powder x-ray diffraction (XRD) patterns of LiNi1/2-xMgxMn1/2 O-2 show fairly sharp (1/3,1/3, L) superlattice reflections (L=0,1,2,3) indicating an in-plane [root 3 x root 3] R30 degrees-type ordering and the almost regular layer stacking with some staking faults. The XRD patterns of LiNi1/3-x mg(x)Co(1/3)Mn(1/3)O(2), do not show the sharp superlattice peaks, but show diffuse scatterings with a intensity maximum at around 2 theta = 21 degrees corresponding to the (1/3,1/3,0) superlattice reflection of an in-plane [root 3 x root 3] R30 degrees-type ordering. Electron diffraction patterns also indicate that the [root 3 x root 3] R30 degrees-type ordered layers are stacked almost randomly in LiNi1/3-xMgxCo1/3Mn1/3O2.