TEM Observation of Shi Track Interaction and Induced Strain in Zirconia at Intermediate Fluences

Abstract

The SHI irradiation of m-zirconia at low fluences in the non-overlapping regime has been shown to produce single ion tracks containing tetragonal (t-zirconia) segments by direct observation by imaging in a transmission electron microscope (TEM). The stability at RT of the high temperature t-zirconia phase is a function of a numerous thermodynamical parameters which include particle size and shape, interfacial energy, oxygen vacancies and strain energy. The absence of strain at low SHI fluence indicates the possibility the presence of oxygen vacancies to be the predominant factor for RT stabilization. However, the increase of fluence into the intermediate range, up to the onset of the overlapping regime, corresponds to the increased strain in the material between the tracks as shown by TEM imaging. At a fluence of 1 x 10 13 cm-2 the tracks are no longer visible due to the excessive strain in the material. Regions of different phases are observed which possibly indicate the onset of phase evolution at this fluence. It is therefore proposed that the stabilizing factor for non-overlapping fluences is due to the presence of oxygen vacancies. However, with increasing fluence into the overlapping regime these oxygen vacancies are possibly annealed out with the predominant factor for the stabilization of the t-zirconia phase being due to the increased strain in the m-zirconia