X-ray diffraction study of elemental thulium to 86 GPa*

We have studied the structures and equation of state of elemental thulium up to 86 GPa in a diamond anvil cell using angular-dispersive x-ray powder diffraction methods at the Advanced Photon Source. This is part of a study of phase transitions in the lanthanide-series metals using cyclohexane as a quasi-hydrostatic medium. We present evidence of a series of phase transitions that appear to follow the anticipated hcp $\to $Sm-type $\to $ dhcp $\to $ distorted fcc sequence of transitions and show the equation of state derived from the x-ray fit data.