Zr–Ce oxide films were made by reactive dc magnetron cosputtering. The elemental composition was determined by Rutherford backscattering spectrometery and the crystalline structure by x-ray diffraction. Li intercalation/deintercalation was accomplished potentiodynamically in a liquid electrolyte. The films remained fully transparent irrespective of their degree of lithiation, which may be reconciled with a population/depopulation of Ce 4f levels.