Phases that exist beyond their thermodynamic fields of stability are important to emerging technologies. Metastable phases are prevalent in far-from-equilibrium processing approaches and often exhibit desirable chemical and physical properties. However, there is limited understanding of the atomic-scale structural mechanisms that allow metastable phases to be recovered to ambient conditions. Metastability plays an important role in the synthesis of different zirconia (ZrO2) polymorphs. We utilized a state-of-the-art analytical approach with neutrons from the world’s most intense pulsed neutron source to investigate the atomic-scale recovery process and the structural properties of the metastable tetragonal phase. Grain-size reduction to the nanometer range and bombardment with high-energy (GeV) ions were used to prepare this metastable form of zirconia. We show in this presentation that the formation of a hierarchical network of nanoscale domains of lower symmetry, separated by domain walls, is the underlying structural mechanism that provides the pathway to the metastable state.