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The radiation-induced monoclinic-to-tetragonal phase transition in ZrO2 and HfO2 has been the subject of many investigations, but the transformation pathways and underlying structural mechanisms are still not well understood. In this study, microcrystalline powder samples of ZrO2 and HfO2 were irradiated with 946 MeV and 1470 MeV Au ions to a wide fluence range up to 3 × 1013 ions/cm2. To characterize beam-induced structural modifications across all spatial length scales, complementary experimental techniques such as synchrotron X-ray diffraction and spallation neutron total scattering were used. The phase evolution of the tetragonal polymorph with increasing ion fluence is accurately described by a heterogeneous track-overlap model that incorporates both direct- and double-impact processes [1]. These damage accumulation processes are an expression of a core-shell ion track morphology that depends on irradiation conditions and target material. Neutron pair distribution function analysis revealed that ion-beam-induced tetragonal ZrO2 is merely a configurational average of short-range orthorhombic (Pbcn) domains stabilized by a dense network of domain walls [2]. This knowledge is critical for a better understanding of how crystalline-to-crystalline phase transformations proceed at the atomic scale under extreme conditions.
[1] A.P. Solomon, E.C. O’Quinn, C.C. Overstreet, P. Simon, C. Trautmann, C.Y. Park, D. Sprouster, G. Baldinozzi, and M. Lang, Multi-Scale Structural Analysis of Swift Ion-Irradiated ZrO2 and HfO2, Acta Materialia A 306, 121926 (2026)
[2] A.P. Solomon, E.C. O’Quinn, J. Liu, I.M. Gussev, X. Guo, J. Neuefeind, C. Trautmann, R.C. Ewing, G. Baldinozzi, and M. Lang, Atomic-scale structure of ZrO2: Formation of metastable polymorphs, Science Advances 11, eadq5943 (2025)