  We use powder neutron diffraction to study the spin and lattice structures of
polycrystalline samples of nonsuperconducting PrFeAsO and superconducting
PrFeAsO0.85F0.15 and PrFeAsO0.85. We find that PrFeAsO exhibits an abrupt
structural phase transitions at 153 K, followed by static long range
antiferromagnetic order at 127 K. Both the structural distortion and magnetic
order are identical to other rare-earth oxypnictides. Electron-doping the
system with either Fluorine or oxygen deficiency suppresses the structural
distortion and static long range antiferromagnetic order, therefore placing
these materials into the same class of FeAs-based superconductors.
