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

TL;DR

This study uses the LDA+U approach to investigate the optical absorption features of polycrystalline HfO2, revealing that the shoulder in the dielectric function is controlled by Hf-O bond length, with implications for high-pressure measurements.

Contribution

It demonstrates that the shoulder-like structure in HfO2's dielectric function is determined by Hf-O bond length, regardless of crystal structure, using LDA+U calculations.

Findings

The shoulder in the dielectric function is linked to Hf-O bond length.

The existence of the shoulder is consistent across different polymorphs.

High-pressure simulations support the bond length's role in optical features.

Abstract

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 directly 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.