TWo dimensional diffusion D 4 3. Three dimensional diffusion simple cubic D=6 FCC(a-Fe D A[(simple cubic: 2. Two dimensional diffusion. 3. Three dimensional diffusion. 2 4 1 D = a FCC(  − Fe ): 2 2 12 1 ) 2 ( 12 4 a a D =  =  2 2 1 6 1 D = a