We report preliminary results from an ongoing study of iron nitride grains formed in high purity iron under nitrogen ion bombardment. Under various implantation conditions, different iron nitride phases grow large enough to produce sharp x-ray diffraction lines. We have used these lines to examine the influence of target temperature during implantation. Between 200°C and 400°C increasing target temperature, which enhances dopant mobility, reduces the retained dose of nitrogen and restricts the formation of nitride phases. Over this temperature range, however, increasing vacancy mobility favors the growth of nitride grains and x-ray line breadth data suggests an optimum temperature for growth of Fe4N grains.