α-MnO2 under pressure: Possible route to δ-MnO2

Structural, electronic and magnetic properties of alpha-MnO2 subjected to pressure are studied using first principles electronic structure calculations. alpha-MnO2 is found to transform to the delta-MnO2 polymorph at similar to 66 GPa of hydrostatic pressure. This comes as an interesting addition to the list of proposed transitions from non-layered to layered structures at high pressure. Unlike transition metal mono-oxides, alpha-MnO2 does not undergo any magnetic collapse up to this pressure. The pristine delta-MnO2 formed this way does not have intercalated ions or molecules, unlike delta-MnO2 synthesized by thermal treatment of KMnO4, but is found to be dynamically stable. This suggests that intercalation is not essential for its stability.