Structural and magnetic properties of chromium dioxide at high pressures

Ab initio calculations were performed on CrO2 to study its behavior and possible similarity to silica under high pressures. At the rutile→CaCl2-type phase transition, the lattice constants, cell volume and total energy change continuously, indicating the second-order nature of the phase transition, consistent with the experimental observations. The current calculations have demonstrated that the rutile→CaCl2-type phase transition is driven by the softening of the Raman active B1g mode, weakly coupling with the elastic shear modulus Cs. Further phase transitions of CrO2 to denser packed phases of α-PbO2-type and pyrite have been well predicted by total energy calculations. Our electronic calculations revealed that CrO2 is still a half-metallic ferromagnet up to pressure of 95 GPa. The present results confirm the analogy of the phase sequence between silica and CrO2 at high pressures.