New beta(fcc)-cobalt to 210 GPa

We report a new phase transition in cobalt from the magnetic epsilon(hcp) t o a beta(fcc) phase, likely nonmagnetic, at 105 GPa. It occurs martensitica lly in an extended pressure region between 105 and 150 GPa without any appa rent volume change. The fee phase of Co is in systematic accordance with th e id and 5d counterparts. The pressure-volume isotherm of beta-Co resembles those of alpha(fcc)-Ni and epsilon(hcp)-Fe within 1%. The phase diagram of cobalt suggests that the fee stability increases with increasing occupancy of d-band electrons from Fe to Co to Ni.