4. For diffusion of interstitial atoms in bcc D=aTo=aTa For tetrahedral interstitial a For octahedral interstitial a' 40—4 6 D=(=) 62244. For diffusion of interstitial atoms in BCC 2 2  D = =a For tetrahedral interstitial For octahedral interstitial 4 1  = 4 0  = 2 2 24 1 ) 2 ( 6 1 6 2 1 a a D a      = =  = =