Variation of TiO2/SiO2 mixed layers induced by Xe+ ion irradiation with energies from 100 to 250 keV

•The atomic mixing occurred at TiO2/SiO2 interface after being irradiated with Xe+ ions of energies from 100 to 250 keV.•The mixing amount increases with ion energy, as evidenced by a decrease in the FWHM of TiO2 peaks and an increase in the thickness of TiO2/SiO2 transition layers.•The mixing amount is proportional to the number of displaced atoms, whereas the ion energy transfer to target atoms plays a crucial role in the inward broadening of mixed TiO2/SiO2 layers.•The refractive index n and the extinction coefficient k of mixed TiO2/SiO2 layers increase after irradiation with Xe ion up to 200 keV, then decrease for 250 keV.