Due to its outstanding electronic and dielectric properties, hafnium dioxide (HfO2) has emerged as a promising material across diverse fields, from high-κ dielectrics to next-generation non-volatile memories and optical devices. A comprehensive understanding of the dielectric response and electronic excitation characteristics of HfO2 is essential for both fundamental studies and device applications. Electron energy-loss spectroscopy (EELS), a key technique for probing dielectric behavior and electronic structure, plays a crucial role in characterizing polymorphic HfO2. In this study, the low-loss and core-loss EELS spectra of cubic (c), tetragonal (t), monoclinic (m) and orthorhombic-III (oIII) HfO2 are systematically investigated using first-principles calculations. In the low-loss region, anisotropic EELS spectra are obtained via time-dependent density functional theory (TDDFT) with random phase approximation (RPA) and adiabatic local density approximation (ALDA), including local-field effects (LFEs), and the influence of finite momentum transfer on the energy and intensity evolution of characteristic excitations is thoroughly examined. In the core-loss region, anisotropic O K-edge energy-loss near-edge structures (ELNES) are calculated using a core-excited pseudopotential approach incorporating core-hole effects. The spectral features are analyzed in conjunction with the projected density of states (PDOS) to elucidate their electronic origins, and the roles of local chemical coordination on the ELNES are further assessed. This work offers rigorous theoretical insight into the electronic excitation properties of polymorphic HfO2. The findings provide a deeper understanding of electronic excitation behavior and dielectric response in different HfO2 polymorphs, thereby advancing the interpretation of their EELS spectra and supporting the optimization of HfO2-based electronic devices.
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