Stability and the equation of state of α-manganese under ultrahigh pressure

We have performed angle dispersive synchrotron-radiation x-ray powder-diffraction experiments on {α}-Mn up to 190 GPa at room temperature by using a diamond-anvil cell and an imaging plate. We have obtained evidence for a structural phase transition in Mn above 165 GPa. A new diffraction peak appeared above 165 GPa, which can be most likely indexed to the 110 reflection of a body-centered-cubic structure. The volume reduction associated with the structural phase transition was estimated to be 2%. The bulk modulus and its pressure derivative of {α}-Mn were determined as B₀=158 GPa and B₀^'=4.6, respectively. The pressure dependence of the bulk modulus indicates the decrease of the magnetic moments of Mn under pressure.