The effect of oxygen deficiency on the structural phase transition and electronic and magnetic properties of the spinel

Abstract

The effect of oxygen deficiency on a phase transition from cubic to tetragonal phase has been investigated for the spinels with by measurements of differential scanning calorimetry (DSC), magnetic susceptibility nuclear magnetic resonance ( NMR) and electronic resistivity . According to the DSC measurements, the transition temperature for a stoichiometric compound is determined to be K. As increases from zero to 0.066, the magnitude of is found to decrease by about 4 K; then, the magnitude of increases by about 41 K with further increase of up to 0.10; thus, the curve exhibits a broad minimum at around . This relationship between and is also observed by the measurements of NMR and . The dependence of on is considered to be a result of a competition between a decrease in the average valence of Mn ions and a dilution of the nearest-neighbour interaction between Mn ions. Both effects are caused by the oxygen deficiency; the former raises , whereas the latter reduces it.

Magnetic properties of lithium intercalation compounds

“…Frozen spin was also observed in a neutron diffraction study by Oohara et al [32]. Magnetic susceptibility measurements were also made on oxygen-deficient spinel LiMn 2 O 4−δ (δ=0-0.1) [33].…”

Evidence of a Cationic Substitution Domain in Lithium-Manganese Spinels

“…may be considerably more interesting for tuning specific physical properties. Indeed, a recent study [11] concerned the effects of oxygen deficiency on the structural phase transition of this compound. By contrast, it is not yet clear whether a not-negligible domain of cationic substitution can exist in the Li-Mn spinel structure.…”

The Sintering Temperature Effect on Electrochemical Properties of LiMn2O4

“…One of the possible causes for this contradictory finding appears to be the difference in the relative amount of Mn ions (Mn 2+ , Mn 3+ , Mn 4+ ) in the LiMn 2 O 4 particles when produced at different temperatures. 10 To investigate the oxidation state of Mn ions in the LiMn 2 O 4 particles, the lattice parameter of LMO700, LMO 800, LMO 830, and LMO870 was calculated from the XRD data ( Table 2). The lattice parameter tended to increase at higher temperatures, whereas the lattice parameters from the particles produced at > 800 o C did not change considerably with the heat treatment temperature.…”

“…8 It induces a change in the mean charge state of the Mn ion, alters the lattice parameter, and deteriorates the electrical properties. 9,10 On the other hand, Mn dissolution reduces the amount of active materials after a reaction with the electrolyte, which is represented by the Hunter's reaction 11 ; 2LiMn 2 O 4 + 4H + = 3λ-MnO 2 + Mn +2 + 2Li + + 2H 2 O. The proton in the chemical reaction is supplied as a byproduct of the chemical reaction of LiPF 6 in the electrolyte and water molecules, and Mn +2 ions are produced from the reaction; 2Mn +3 = Mn +2 + Mn +4 .…”