Structural transition in Mg-doped LiMn2O4: a comparison with other M-doped Li–Mn spinels

The charge distribution in the Mg-doped lithium manganese spinel Li1.02MgxMn1.98−xO4 with 0.00<x≤0.20 is discussed and compared to those pertinent to other M-doped samples (M=Ni2+, Co3+, Cr3+, Al3+ and Ga3+). EPR spectra, low temperature X-ray diffraction and conductivity data are related to the cooperative Jahn–Teller (J–T) transition occurring at about 280 K in the undoped sample. nsitivity of the cationic sublattice in displaying electronic and magnetic changes after substitution is remarked. The inhibition of the J–T transition is related to the ratio r=|Mn4+|/|Mn3+| as deduced from the charge distribution model [Li1−xt+Mgxt2+]tetr[Liy+xt+Mgxo2+Mn1−3y−2x3+Mn1+2y+x4+]octa where x=xo+xt. For y=0.02 and x=0.02, a value r=1.177 is obtained, very close to rlim=1.18, the limit value beyond which the transition is inhibited.