Octahedral 0 N/ K 1 1 1 2 2 2 al - - - Tetrahedron - 1 3 1 4 4 4 (a)Carbon diffuses in iron Via an interstitial mechanismfor FCC iron from one octahedral site to an adjacent one. In Section 4. 3 (Figure 4. 3a) we note that two general sets of point coordinates for this site are 0%1 and E ii' Specify the family of crystallographic directions in which this diffu- sion of carbon in FCC iron takes place