On the structural phase transitions in ferroelectric hafnia

Hafnia (HfO₂) has emerged as a promising material for ferroelectric device applications due to its robust ferroelectricity at nanoscale dimensions, high-κ dielectric behavior, and seamless integration with complementary metal-oxide-semiconductor (CMOS) technology. Despite possessing a nonpolar ground state and several competing nonpolar, low-energy stable phases in its bulk form, the ferroelectric phase of hafnia is associated with the stabilization of a metastable, non-centrosymmetric orthorhombic phase (Pca2₁). This metastable phase can be realized by controlling factors such as doping, film thickness, strain, and other crystal-growth conditions. In this work, we perform first-principles calculations to investigate the structural phase transitions in hafnia, focusing on the key mechanisms that facilitate the stabilization of its ferroelectric orthorhombic phase. The complex interplay between structural phase transitions, defects, and material properties is analyzed, offering insights into optimizing ferroelectric performance for applications in non-volatile memory and other ferroelectric devices.