Local structure and defects in ion irradiated KTaO₃

The modification of the local structure in cubic perovskite KTaO₃ irradiated with 3 MeV and 1.1 GeV Au ions is studied by Raman and x-ray absorption spectroscopy, complemented by density functional theory (DFT) calculations. In the case of irradiation with 3 MeV Au ions where displacement cascade processes are dominant, the Ta L₃-edge x-ray absorption measurements suggest that a peak corresponding to the Ta-O bonds in the TaO₆ octahedra splits, which is attributed to the formation of Ta_K antisite defects that are coupled with oxygen vacancies, V _O. This finding is consistent with the DFT calculations. Under irradiation with 1.1 GeV ions, the intense ionization and electronic energy deposition lead to a blue shift and an intensity reduction of active Raman bands. In the case of sequential irradiations, extended x-ray absorption fine structure measurements reveal a decrease in concentration of coupled Ta_K-V _O defects under subsequent irradiation with 1.1 GeV Au ions.