14) [5 marks] Consider a piece of Aluminum inside a furnace. a) Unit cell: Draw its ball-stick model, cross-shade its section with (111), and indicate [021]. Make sure to label all items including atom sites, axes, and origin. b) The fraction of vacant sites over all possible atom sites in the piece is 2.47%x10-5. i) Determine the temperature of the material. Give the result in C. Use Ev=0.76 eV. ii) Calculate the density of vacant sites. Give the result in m~3