The evidence for the occurrence of two successive transitions in Al2O3 from the analysis of Hugoniot data
Juichiro Hama, Kaichi Suito
We calculated the Hugoniots of Al2O3 to 400 GPa using a thermoelastic model developed previously and compared the results with measurements. The P H – rH data and U – u data for crystalline corundum by McQueen and Marsh agree well with our results calculated by the elastic – plastic model to 130 GPa, while Marsh’s later data lie in between ours obtained by the elastic – plastic model and those obtained by the elastic – isotropic model to 130 GPa. Above 130 GPa, the P H – rH data of the two sets of measurements begin to depart towards the higher-density side. On the other hand, the Hugoniot data of Mashimo et al to 104 GPa agree well with ours obtained by the elastic – isotropic model, suggesting rapid relaxation of shear stress. The first two experiments (flash-gap method) revealed no phase transitions, but the third one (inclined-mirror method) showed a phase transition at 79.3 GPa. The discrepancy can be largely attributed to the measurement method. Incorporating the theoretical values of the elastic quantities and cohesive energy in the static lattice at zero pressure.