A small shoulder of optical absorption in polycrystalline HfO₂ by LDA+U approach

The dielectric function of the wide-gap optical material HfO₂ is investigated by the local density approximation (LDA)+U approach. We focus on the origin of the shoulder-like structure near the edge of the band gap in the imaginary part of the dielectric function, which has been observed on the thin films of monoclinic HfO₂. A comparison study on the three polymorphs of hafnia shows that regardless of the underlying crystal structure, the existence of the shoulder is mainly controlled by the value of the shortest length of Hf–O bonds. The proposition is further supported by the numerical simulations of isostatic pressing. A possible implication in high-pressure measurements is suggested accordingly.