Local-symmetry distortion, optical properties, and plasmonic states of monoclinic Hf0.5Zr0.5O2 system: a density-functional study

Abstract

We study structural, electronic, and optical properties of the monoclinic Hf0.5Zr0.5O2 (space group: P21/c). Monoclinic ZrO2 and HfO2 systems are used as the references. This study employs the plane-wave density-functional method within the generalized gradient approximation. The structural properties emphasize the strongest local-symmetry distortion in Hf0.5Zr0.5O2 system. The bandgap (3.67 eV) and valence bandwidth (∼4.94 eV) of the system are between that of ZrO2 and HfO2 systems. Furthermore, the negative average defect formation energy confirms the stability of Hf0.5Z0.5O2 system. In all the systems, the significant differences between n0x(n0y) and n0z imply the strong optical dichroism between xy plane and z axis. On the other hand, the small differences between n0x and n0y imply the weak optical dichroism along xy plane. In Hf0.5Zr0.5O2 system, the optical properties show the zero-frequency refractive indices of (n0x, n0y, n0z) = (2.039, 2.086, 1.851). The system also shows the highest intensity and weakest dichroism of plasmonic states along y axis and xy plane, respectively. Moreover, we find the lowest energy level of maximum transmittance (T ≈ 1), strong-reflectance width, absorption width, and saturation threshold energy (∼9.6 eV) of the effective number of valence electrons. Our result emphasizes the importance of the doping treatment to the significant tuning of optical properties of Hf1−xZrxO2 system. This study presents the essential properties to guide future experiments to develop novel optical devices.