Low energy Ar+ ion irradiation effects in monoclinic zirconia

Abstract

Argon ion beam induced phase transformation (monoclinic to tetragonal) and bubble formation in monoclinic zirconia (ZrO2) has been studied using grazing incidence X-ray diffraction, electron microscopy, Raman scattering and photoluminescence spectroscopy. Monoclinic zirconia samples were irradiated with low energy (120 keV) Ar+ ions at temperatures 300 K and 143 K. The as-sintered and Ar+ ion irradiated zirconia samples were then irradiated using an excimer laser of wavelength 248 nm (energy 5 eV) to study the defect rich material (after ion irradiation) behavior at extreme condition (where ionization process is dominant). Zirconia was found to undergo a partial phase transformation from monoclinic to tetragonal (≈20%; ion fluence 2 × 1017 ions/cm2) upon Ar+ ion irradiation at 143 K. Further, Ar bubbles were formed and the size of the bubble is found to increase with the ion fluence, irrespective of sample temperature during ion irradiation. The oxygen vacancies (produced during ion irradiation) lead to strain field in the sample and this strain field is the prime cause for phase transformation. The rate of phase transformation was found to be faster in case of ion irradiation at 143 K. Further it was observed that Ar+ ion irradiation lead to creation of defects and laser irradiation on as-sintered zirconia leads to annihilation of defects. However, when laser irradiation was carried out on ion irradiated zirconia, there is a competition between production and annihilation of defects where the production of defects by the Ar+ ion irradiation is a dominant one. Further, the present work confirms the role of O vacancy in the monoclinic to tetragonal phase transformation and the results are consistent with the earlier report (Simeone et al., 2000).