lattice perfect lattices helical 13b spirals 13a formed
sf lattice fcc stacking intrinsic extrinsic
stacking intrinsic sequence extrinsic fcc lattice hcp
stacking fault fcc planar abcabc faults hcp atoms
sic stacking 15r sequences 6h 4h dislocation
stacking sequence fcc fault planes closest packed hcp bcc atoms layer