Inhibition of Jahn-Teller cooperative distortion in LiMn2O4 spinel by Ga3+ doping

Ga-doped Li-Mn-spinels Li1.02GaxMn1.98-xO4 with 0.00 less than or equal to x less than or equal to 0.20 are investigated to verify the lattice capability to allocate the Ga3+ ions on both tetrahedral and octahedral sites and to determine the lowest amount of dopant that prevents the occurrence of the Jahn-Teller (J-T) transition observed near room temperature in LiMn2O4. XRPD, NMR, and EPR spectra and static magnetic susceptibility and conductivity data are related to the site occupancy, the Mn valence state and the homogeneous distribution of the dopant. The electronic and magnetic features of the spinel framework are strongly dependent on substitution in its cationic sublattice: dopant amounts as low as 1% significantly modify the temperature of the conductivity drop associated with the J-T distortion. Ga3+ ions substitute chiefly in the octahedral sites, Mn4+ ions occupy regular and distorted octahedral sites and, at the same time, the value of lattice parameter remains unchanged. Mn2+ ions are present in the tetrahedral site and Li+ increases in the octahedral site as a consequence of Li-Mn/Ga inversion. Such a mechanism increases the efficiency of J-T inhibition by Ga doping, in comparison with transition cations having the same valence.