MATS 3011 Lecture : Lecture 232014.pdf

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15 Jul 2014
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Atoms touch along edge (1/8)*8 = 1 atom/unit crystal. Bcc crystal structure (-1/8)*8 + 1 = 2 atom/u. c. In bbc, atoms along body-diagonal touch each other length of body-diagonal = 4r, where r is atomic radii. In bcc, 4r = sqrt[3]a --> a = 4r/sqrt[3] Cn in bcc = 8 (# nearest neighbors) # atoms/u. c. in fcc = (1/8)*8 + (1/2)*6 = 4 atoms/u. c. Atomic packing factor: (apf) = (volume of atoms in unit cell)/(volume of unit cell) Apf for fcc = 4((4/3)pir3)/a3 = 4((4/3)pir3)/(2sqrt[2]r)3 = 0. 74 ---> 74% # atoms in unit cell = 8 atoms/u. c. Density calculation density = (total weight)/(total volume) = (n*a)/(vc*na) n = # atoms/u. c. A = atomic mass (gm/mol) vc = volume of u. c. = (total weight)/(total volume) = (4wzn*4ws)/(a3*na) need to find a, do like we did before. Zn and s are making a covalent bond ----> can find distance btwn atoms.

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