This assignment studied both a surface defect in BCC Iron, and a vacancy in FCC and BCC Iron. Iron was chosen because of its crystalline structure and well known crystal structures. Iron is used in thousands of engineering applications most specifically as Steel. Steel being Iron with carbon constituents incorporated. BCC Iron is stiffer than FCC iron because of the crystal structure.
Vacancies are point defects in crystalline materials.
Vacancies are missing atoms from a lattice crystal structure. The number of vacancies and is often determined by the temperature of the material. The higher the temperature the higher the concentration of vacancies in a solid. Vacancies can often be responsible for creep and other failure mechanisms at higher temperatures. Vacancies also allow for impurity atoms to exist in a lattice, which can change material properties.