Decreased electrochromism in Li-intercalated Ti oxide films containing La, Ce, and Pr

Films of Ti–La oxide, Ti–Ce oxide, and Ti–Pr oxide were produced by reactive dc magnetron sputtering. Their composition was determined by Rutherford backscattering spectrometry. X-ray diffractometry and infrared absorption spectroscopy indicated that the microstructure was heavily disordered and in most cases Ti-oxidelike. Electrochemical Li intercalation/deintercalation was studied by cyclic voltammetry, and ensuing optical data were recorded by spectrophotometry. Ce addition diminished the electrochromism, and films with Ce/Ti atom ratios exceeding 0.3 were almost fully transparent irrespective of their lithiation, pointing at the potential applications of such films as counter electrodes in transparent electrochromic devices. The optical and electrochemical data were discussed in terms of a model based on electron insertion/extraction in $\text{4f}$ states located in the gap between the valence and conduction bands of ${\mathrm{CeO}}_{\mathrm{2}}.$