Light ion irradiation-induced phase transformation in the monoclinic polymorph of zirconia

Ion irradiation damage experiments were performed at ∼80 K on polycrystalline samples of monoclinic, slightly sub-stoichiometric zirconia (ZrO_1.98). Following irradiation with 150 keV Ne⁺ ions, the monoclinic phase was gradually replaced by a new phase. Transmission electron microscopy (TEM) observations in cross-sectional geometry and electron microdiffraction (μD) measurements revealed that the irradiated layer in a sample irradiated to a fluence of 5 × 10²⁰ Ne/m² is partially transformed to a higher symmetry phase of high crystallinity. This phase transformation is accompanied by reduction of the initial micron-sized, highly-twinned grain distribution, to a nano-phased grain structure. Grazing incidence X-ray diffraction (GIXRD) measurements revealed that the radiation-induced phase is a tetragonal polymorph of zirconia. This was verified by the existence of strong (1 0 1) diffraction maxima and weak (1 0 2) reflections (body-centered cell). Raman spectroscopy (RS) measurements were also performed in an attempt to corroborate GIXRD results obtained from the irradiated material. RS measurements in the confocal geometry agreed with GIXRD measurements, although RS was not as definitive as GIXRD. In addition to RS showing the existence of a band corresponding to a tetragonal structure at 262 cm⁻¹, a new mystery band appeared at 702 cm⁻¹ that increased in intensity as a function of irradiation fluence.