Structural, magnetic and electronic properties of CrO₂ at multimegabar pressures

As the only half-metallic ferromagnetic material in 3d transition metal dioxides, CrO₂ has attracted great scientific interest from materials science to physical chemistry. Here, an investigation into the structural, magnetic and electronic properties of CrO₂ under high pressure has been conducted by first-principles calculations based on density functional theory. Static calculations have predicted that CrO₂ undergoes structural transitions with the sequence of rutile-type → CaCl₂-type → pyrite-type → Pnma → (Fe₂P-type→) I4/mmm at high pressures. In addition, a transition from the ferromagnetic state to the non-magnetic state with the magnetic collapse of Cr is observed in CrO₂ at the pyrite-Pnma transition. This transition also delocalizes the 3d electrons of Cr and leads to a metallic character of CrO₂. The equation of state, elasticity and band gap for each energetically favorable phase of CrO₂ are determined. Our results not only bridge the gap about the high-pressure behavior of CrO₂ in previous studies but also extend our understanding of its properties up to multimegabar conditions. According to previous data and present results, we further discuss and summarize the high-pressure behavior of various AO₂ compounds. This can contribute to investigating properties of other AO₂ compounds or exploring novel materials at high pressures.