Defect Chemistry of Hafnia-Based Ferroelectrics under Oxide-Electrode Constraints

Abstract

HfO$_2$ heterostructures with La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) epitaxial electrodes have attracted interest as ferroelectric systems with electrode-dependent defect chemistry. However, the formation and stability of defects under LSMO-constrained chemical conditions remain poorly understood. In this work, we use density functional theory calculations to systematically investigate oxygen vacancies and La-, Sr-, and Mn-related interstitial and substitutional defects in HfO$_2$ under chemical environments constrained by the LSMO electrode. We find that LSMO stability substantially narrows the accessible O chemical potential range relative to bulk HfO$_2$, altering the predicted defect formation energies. While La and Sr substitutional defects are governed primarily by preferred ionic valence states, oxygen vacancies and Mn substitutional defects exhibit charge states sensitive to the local atomic environment. In addition, defect-complex calculations in orthorhombic HfO$_2$ reveal negative binding energies, indicating favorable defect association. The La- and Mn-related defect complexes exhibit thermodynamic competition, with their relative stability depending on the Fermi level and oxygen chemical potential. Lastly, extending the analysis to Hf$_{0.5}$Zr$_{0.5}$O$_2$ and ZrO$_2$ reveals common oxygen-vacancy trends, while the stability of LSMO-derived defects depends more strongly on the host material and crystal phase. These results provide a thermodynamic basis for understanding how electrode-constrained chemical environments and host structures influence defect formation, charge compensation, and defect-complex stability in HfO$_2$-based materials.