Infrared-active phonons inCr2O3

Abstract

We have identified serious errors in a previously published assignment of the ir-active phonons for the $\alpha$-corundum structured crystal ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$. We have measured the ir-reflectance for the two principal polarizations, $\overrightarrow{\mathrm{E}}\perp \overrightarrow{\mathrm{c}}$ and $\overrightarrow{\mathrm{E}}\parallel \overrightarrow{\mathrm{c}}$, and have obtained the properties of the ir-active long-wavelength vibrations—the TO- and LO-phonon frequencies, the contributions of the phonon-modes to the static dielectric constant and the damping. These are then compared with other $\alpha$-corundum structured sesquioxides, $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{Ti}}_2{\mathrm{O}}_3$.