Thermal evolution of infrared vibrational properties ofLi4/3Ti5/3O4measured by specular reflectance

Abstract

The thermal evolution of the vibrational properties of a powdered sample of ${\mathrm{Li}}_{4/3}{\mathrm{Ti}}_{5/3}{\mathrm{O}}_4,$ synthesized by a solid-state reaction at 800 °C, from room temperature to 483 K (210 °C), has been studied by near normal IR reflectance spectroscopy. Although the x-ray-diffraction pattern of this sample can be indexed in a cubic cell, $a=8.3613\mathrm{}\left(7\right)\mathrm{}\AA ,$ space group $\mathrm{Fd}3m,$ 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 $8a$ 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.