bulk single crystal*

HfO₂-based materials attract a lot of research interest because the rich polymorphism, including several metastable phases, results in intriguing physics properties and potential for applications. However, the absence of certain phases in the bulk sample hinders a deeper understanding. Here, we report that the high-quality HfO₂ single crystals have been successfully grown by a state-of-the-art laser-diode-heated floating zone (LDFZ) technique. Metastable phases have been stabilized, which is sensitive to dopants and thermal treatments. X-ray, TEM, and neutron diffraction are performed for a comprehensive structural phase diagram. DFT calculations elucidate the energy paths of phase formation and emphasize the crucial factors in the stabilization of metastable phases. Our study of bulk HfO₂ single crystals uniquely unveils the rich structural physics, including domain and domain wall nature, and paves a new essential road for future study of HfO₂-based materials.