Theoretical study on dielectric response of amorphous alumina

Abstract

Amorphous ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ model structures are theoretically generated at the atomistic level, and their structural, electronic, and dielectric properties are investigated by first-principles calculations. Results show that the model structures have Al atoms having lower coordination numbers than that of Al atoms in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, and that the coordination number lowering leads to a band-gap reduction relative to the crystal band gap. Calculated dielectric constants of the model structures, originating from electronic and lattice polarization, are in good agreement with experimental values. Focusing attention on the lattice polarization contribution to a dielectric constant that is predominant over the electronic one, we found that there are some atomic sites dominantly contributing to the lattice dielectric constant in the amorphous model structure.