First-principles calculations on the pressure induced zircon-type to scheelite-type phase transition of CaCrO4

The zircon-type and scheelite-type CaCrO4 are investigated by first-principles calculations based on density-functional theory. The calculated zircon-type lattice parameters and the oxygen positions are in agreement with the experimental results and those of scheelite-type structure are studied for the first time in this work. The theoretical phase transition pressure of CaCrO4 from zircon phase to scheelite phase is about 5.8 GPa, which is consistent with the experimental observation. From the density of states and the electronic band structures, CaCrO4 is an insulator with a direct band gap (2.16 eV) for zircon-type structure and an indirect band gap (1.98 eV) for scheelite-type structure. The bulk moduli of the two phases are evaluated from the Murnaghan equation fit to the total energies as a function of the unit cell volume.