First-principles study of high-pressure alumina polymorphs

We investigate by first principles the structural properties and relative stability of six alumina polymorphs, namely: corundum, (Formula presented) (II), (Formula presented) perovskite, (Formula presented)-perovskite, (Formula presented)-type rare-earth sesquioxide, and (Formula presented)-type rare-earth sesquioxide. The compressive behavior and pressure-induced changes in the local environment of different aluminum sites are investigated in detail for corundum, (Formula presented) (II) and the perovskite phases, which are the predicted stable phases within the pressure range of 0-450 GPa. This information is crucial for understanding the electronic states of a (Formula presented) color center in alumina (ruby) and the resulting intra-(Formula presented) transitions, i.e., the ruby fluorescence. Implications of these pressure-induced phase transitions in (Formula presented) to the ruby fluorescence pressure scale are discussed.