Cation distribution and phase transformations in LiMn2−yTiyO4 solid solutions

Series of lithium manganese titanium spinel-like oxides LiMn2−yTiyO4 (0.2⩽y⩽1.5) were synthesized by solid state reaction carried out at 1100 °C, followed by slow cooling to a particular temperature, depending on the titanium content y, and then air-quenched to room temperature. The procedure has permitted to obtain single-phase products. The samples have been characterized by X-ray powder diffraction (XRD), thermal analysis (TG) and electron paramagnetic resonance (EPR) spectroscopy. Compounds whose composition falls within the interval 0.2⩽y⩽1.0 crystallize in the space group Fd3m, whereas those having y>1.0 crystallize in the space group P4332. Analysis of the structural parameters refined from XRD data revealed that the tetrahedral sites are occupied by Li+ and Mn2+. The end member Li+Mn0.52+Ti1.54+O4, which was synthesized in argon atmosphere, is reported for the first time. It crystallizes in the space group P4332, a=8.4369(1)Å, with all Mn2+ ions being situated at the tetrahedral sites. Its EPR spectrum consists of a Lorentzian-shaped line, centered at g=2.004 with a peak-to-peak width of 25.7 mT. This line has been assigned to Mn2+ ions. Rietveld structure refinement results show that asyincreases from 0 to 1.5 the occupancy factor of Mn2+ in the tetrahedral sites increases from 0 to 0.5, while the occupancy factors of Mn3+ and Mn4+ in the mixed (Mn3+, Mn4+, Ti4+) octahedral sites decrease from 1 to 0.