Influence of Simultaneous Doping of $Li^+$ and $Fe^{3+}$ Ions in the $LiMn_2O_4$ Spinel Structure

A series of compounds $Li_xMn_{3-x-y}Fe_yO_4$ (x=1.0125;0≤y≤0.05) were synthesized by solid state reaction of $Li_2CO_3$ with the manganese oxide or iron-manganese oxide precursors. Investigations of the structure transformation effect of double substitution with $Li^+$ and $Fe^{3+}$ ions in $LiMn_2O_4$, in the temperature range of 10-300 K, were undertaken using high-resolution X-ray powder diffraction at the HASYLAB (DESY) synchrotron. The $Li_{1.0125}Mn_{1.9625}Fe_{0.025}O_4$ transforms from cubic (Fd3̅ m) to orthorhombic (Fddd) below 250 K, and is stable to 10 K. Whereas in the $Li_{1.0125}Mn_{1.9375}Fe_{0.05}O_4$ oxide no phase transition was observed, this spinel remains in cubic structure down to the temperature of 10 K.