Structural and magnetic properties of orthorhombic Li xMnO 2
Abstract
Rietveld refinement of the crystal and magnetic structures of Li xMnO 2 ( x = 0.98, 1.00, 1.02) are performed using neutron and X-ray measurements. A significant structural disorder due to the presence of manganese ions in lithium positions (Mn Li) and lithium ions in manganese ones (Li Mn) is found to be a common feature of Li 0.98MnO 2, Li 1.00MnO 2, and Li 1.02MnO 2. An essential anisotropy of the thermal-expansion coefficients of the lithium manganese oxides is observed in the temperature range of 1.5-300 K. Furthermore, the distortion of the oxygen octahedral environment around the manganese ions decreases when the temperature lowers. This is attributed to the strong exchange interactions between parallel exchange-coupled Mn chains. First-principles calculations of the effective exchange-interaction parameters in Li 16Mn 16O 32 confirm the essential antiferromagnetic interactions between the chains. In addition, a hypothetical (Li 15Mn)Mn 16O 32 structure where a lithium atom located between the Mn double layers is replaced by a manganese atom is considered. The calculations reveal that the presence of such defects results in appearance of a ferromagnetic component that agrees with the magnetic measurements.
- Publication:
-
Solid State Sciences
- Pub Date:
- February 2007
- DOI:
- 10.1016/j.solidstatesciences.2006.11.013
- Bibcode:
- 2007SSSci...9..196K