Thermal evolution of infrared vibrational properties of Li4/3Ti5/3O4 measured by specular reflectance

The thermal evolution of the vibrational properties of a powdered sample of Li4/3Ti5/3O4, synthesized by a solid-state reaction at 800 degreesC, from room temperature to 483 K (210 degreesC), has been studied by near normal TR reflectance spectroscopy. Although the x-ray-diffraction pattern of this sample can be indexed in a cubic cell, a = 8.3613(7) Angstrom, space group Fd3m, the IR reflectance spectra show six vibrational modes in disagreement with the spinel structure previously proposed in the literature. A different structural model has been proposed in which lithium ions, originally placed at ga tetrahedral sites in the spinel structure, partially migrate to the empty 16c octahedral sites. It has been concluded from IR spectroscopy that this migration process increases with temperature. Such a dependence suggests a relationship between the vibrational properties of this material and the hopping mechanism involved in its ionic conductivity.