Non-empirical study on pressure dependence of ruby bond length

Abstract

Due to its potential application in luminescence technologies, the complete understanding on pressure dependence of ruby is especially important. Up to recently, the theoretical prediction on the structural properties of ruby under pressure has been made involving the empirical parameters. Therefore, here we performed a non-empirical study on the pressure dependence of ruby bond length. Due to the Cr3+ substitution and the applied external pressure, the local structure of α-Al2O3: Cr3+ was changed. We estimated this effect by performing the first-principles band-structure calculations using Cambridge Serial Total Energy Package (CASTEP) method and compared with the Shannon’s crystal radii method. The two different bond lengths; Cr-1st nearest neighbour oxygen (d1) and Cr-2nd nearest neighbour oxygen (d2) were investigated in detail. The results show that under 0-110 GPa the d1 and d2 decreased ca. 0.172 and 0.145 Å, respectively. These results were slightly smaller than the d1 and d2 decreases in the case of pure α-Al2O3 crystal, they were observed to be ca. 0.167 Å for d1 and 0.177 Å for d2. In the other words, the d1-d2 differences were larger at the higher pressure, ca. 0.052-0.080 Å for 0-110 GPa.