Thermal expansion in lithium manganese oxide spinels Li[LixMn2−x]O4 with 0 ≤ x ≤ 1/3

Abstract

In order to know the coefficients of thermal expansion in lithium manganese oxide spinels Li[LixMn2−x]O4 with 0 ≤ x ≤ 1/3, X-ray diffraction measurements are performed in the temperature (T) range from 400 to 100 K. The crystal structure for x = 0 changes from the high-T cubic phase (Fd3¯m) into the low-T orthorhombic phase (Fddd) below 285 K due to a cooperative the Jahn–Teller transition. Hence, the average coefficients of linear thermal expansion (αL) in x = 0 are very different between the three orthorhombic axes; αL = 1.3(1) × 10−6 K−1 along the ao-axis, αL = 13.1(1) × 10−6 K−1 along the bo-axis, and αL = 5.7(1) × 10−6 K−1 along the co-axis, where ao, bo, and co are the lattice parameters of orthorhombic phase. On the other hand, the crystal structure for the samples with x ≥ 0.05 keeps the cubic phase (Fd3¯m) down to 100 K. The αL value is almost independent on x at x ≥ 0.05, i.e. αL ∼ 7.0 × 10−6 K−1. This suggests that the bond strength between Mn(Li) and O2− ions does not increase by the partial substitution of Li ions for Mn ions.