Infrared spectroscopy investigation of the charge ordering transition in LiMn2O4

Using infrared spectroscopy we have investigated LiMn2O4 through the charge ordering phase transition taking place around 290 K. We show that the phonon spectrum becomes much more structured below the transition temperature, confirming that the crystal structure is more distorted. The transition is reversible and both the cubic and the orthorhombic phases obtained at room temperature, depending on the thermal history of the sample, are stable. The evolution of the electronic gap confirms that charge carriers localise as temperature decreases down to 100 K, where the electronic properties freeze. This freezing process is not accompanied by structural changes. (C) 1999 Elsevier Science Ltd. All rights reserved.