  The vortex phase diagrams of NdFeAsO0.85F0.15 and NdFeAsO0.85 superconductors
are determined from the analysis of resistivity and current-voltage (I-V)
measurements in magnetic fields up to 9 T. A clear vortex glass to liquid
transition is identified only in the oxygen deficient NdFeAsO0.85, in which I-V
curves can be well scaled onto liquid and glass branches consistent with the
vortex glass theory. With increasing magnetic field, the activation energy U0,
deduced from the Arrhenius plots of resistivity based on the thermally
activated flux-flow model (TAFF), decays more quickly for NdFeAsO0.85F0.15 than
for NdFeAsO0.85. Moreover, the irreversibility field Hirr of NdFeAsO0.85
increases more rapidly than that of NdFeAsO0.85F0.15 with decreasing
temperature. These observations evidence the strong vortex pinning effects,
presumably caused by the enhanced defects and disorders in the oxygen deficient
NdFeAsO0.85. It is inferred that the enhanced defects and disorder can be also
responsible for the vortex glass to liquid transition in the NdFeAsO0.85.
