Chemical and Magnetic Characterization of Spinel Materials in the LiMn2O4–Li2Mn4O9–Li4Mn5O12System

Abstract

Lithium manganospinels belonging to the LiMn2O4–Li2Mn4O9–Li4Mn5O12system were prepared by solid-state reaction of various lithium salts and manganese sources at temperatures ranging from 400 to 900°C. Their exact stoichiometry, which is highly dependent on the preparation temperature, was determined by X-ray diffraction, atomic absorption spectroscopy, and redox titration. Nearly stoichiometric LiMn2O4shows a reversible phase transition at 30°C upon heating and at 10°C upon cooling, which is associated with a tetragonal-cubic transformation. An increase in the average oxidation state of manganese from 3.5+ to 4+ in the two systems Li1−δMn2−2δ(0 ≤ δ≤ 0.11) and Li1+δMn2−δO4(0 ≤ δ ≤ 0.33) results in (i) the suppression of the Jahn–Teller distortion observed around room temperature for stoichiometric LiMn2O4and (ii) a progressive passage from antiferromagnetic (LiMn2O4, θ = − 266 K,nMn+ = 3.5) to ferromagnetic behavior (Li4Mn5O12, θ = + 40 K,nMn+ = 4.0), where the lattice parameter is not too small.