Structural transformation relationship for hafnia ferroelectric phase

The ferroelectricity of hafnia-based thin films with a dominant phase of orthorhombic Pca21 has been reported. However, the relationship of structural transformations between the orthorhombic Pca21 and other hafnia structures remains unclear. In this work, all the structures have been optimized. Then, the fluorite-related structures have been used to analyze the structural relationship. Calculations of the lattice energies and the relative atomic displacements between the structures suggest that the Pca21 phase may originate from the P42/nmc or Pbca phases.