Novel mechanism of ferroelectricity in HfO₂

Ferroelectric HfO₂ has drawn great attention due to its promising properties, such as compatibility with existing silicon technology, and its ability to retain ferroelectricity down to ultra-thin limits. The origin of polarization in HfO₂ is possibly the most important theoretical problem in ferroelectricity, which limits our ability to fully understand and control its behavior in practical applications. The ongoing debate centers on whether HfO₂ is a proper or improper ferroelectric, as it displays traits from both classifications. In this study, we employ symmetry-guided first-principles quantum mechanical (DFT) calculations to achieve an accurate representation of the energy landscape and the minimum energy pathway for phase transitions. This enables us to delve into the microscopic mechanisms governing the phase transitions and clarify the origin of ferroelectricity in HfO₂, which is distinct from any previously considered proper or improper category.