1- The FCC Lattice 1- Place the FCC lattice pattern ("flower" pattern) into the lattice frame so that a crystal model can be started at the lattice origin. 2- Add marbles

to the lattice pattern, building in three coordinate directions. 3. Look at the crystal model you have made and try to determine the basic FCC unit cell. Remember, it must be a repeatable unit in the lattice (see figure below). 4- Using the ruler provided, measure the lattice constant, ag. in millimeters. 5. The marbles (atoms) have a diameter d = 0.5 inches (12.7 mm). Calculate the lattice constant, , for this lattice using d (see figure below). 6- Add or remove atoms from your model until you have developed the atomic plane with the highest atomic density. Calculate the planar atomic packing factor for the plane you constructed. To do that, refer to the last picture below: using d, calculate the surface of the spheres within the rectangle and divide by the surface of the rectangle. Planar Filling Factor = 7- Along which direction is the highest atomic density? (a) Along the cube edge (b) Diagonally across the face of the cube (c) Across the body diagonal (through the center of the cube) 8- Determine the coordination number, CN, for atoms in this crystal lattice. The coordination number is the number of atoms that one atom in the lattice touches. CN= 9. Determine the number of atoms there are in each unit cell (remember that some atoms are shared between adjacent unit cells). Atoms/U.C. 10-Calculate the packing factor for this crystal lattice (using d, calculate the volume of the spheres within the cube and divide by the volume of the cube). packing factor=/n2. The HCP Lattice 1- Place the HCP lattice pattern ("flower" patter) into the lattice frame so that a crystal model can be started at the lattice origin. 2- Add marbles to the lattice pattern, building in three coordinate directions. NOTE: Pay close attention to the difference in stacking between FCC and HCP structures shown previously (see previous page). 3- Look at the crystal model you have made and try to determine the basic HCP unit cell. Refer to the figures below for the geometry of the unit cell, as it is hexagonal rather than cubic. The a, parameter corresponds a side of the base hexagon and the c parameter to the tall edge of the unit cell. 4- Using the ruler provided, measure the lattice constants, q, and c, in millimeters. mm mm 5- Along which direction is the highest atomic density? (a) In the basal plane along to the a-axis (b) In the basal plane perpendicular to the a-axis (c) Along the c-axis 6- Determine the coordination number, CN, for atoms in this crystal lattice. 7- Determine the number of atoms there are in each unit cell (remember that some atoms are shared between adjacent unit cells). Atoms/U.C. 8- Calculate the packing factor for this crystal lattice (using d, calculate the volume of the spheres within the cube and divide by the volume of the cube). packing factor 9- Add or remove atoms from your model until you have developed the atomic plane with the highest atomic density. Calculate the planar atomic packing factor for the plane you constructed. To do so, refer to the last picture below: using d, calculate the surface of the spheres within the rectangle and divide by the surface of the rectangle. Planar Filling Factor = 10-Which of the other lattices that you have encountered does the HCP highest-packed plane resemble? None FCC BCC