Abstract :
The stability field of the Li–Mn–O spinel,
Li1 + xMn2 – xO4 – d, was investigated as a function of
temperature, T, cation composition, nLi/nMn, and oxygen
partial pressure, pO2, by means of in situ X-ray
diffraction (XRD) and thermogravimetry (TG). In a
T-nLi/nMn phase diagram, the stability field is described
by the upper and lower critical temperatures, Tc1 and
TcL, respectively. Above Tc1, Li2MnO3 is formed as a
second phase, and below TcL Mn2O3 is formed. Both
Tc1 and TcL decrease continuously with increasing nLi/
nMn and increase with increasing pO2. The single phase
region contains lithium-deficient and lithium-excess
spinels, and no discontinuous change of the critical
temperature curves was found at nLi/nMn = 0.5, corresponding
to LiMn2O4. With the experimental data
obtained in this work, a three-dimensional stability
field of the Li–Mn–O spinel phase diagram is put
forward to describe the relationship between T, nLi/
nMn and pO2. In addition, the upper critical temperature,
Tc1, was investigated for spinels doped with Ni,
Co and Mg. For all three dopants, Tc1 decreases with
increasing dopant concentration.
