Question

2. Elemental Si crystallizes with a diamond cubic structure is shown at right below. The Si atoms form an foc unit cell with a certain fractions of the tetrahedral sites occupied. a) How many octahedral sites_ and how many tetrahedral sites____ are there per unit cell. How many tetrahedral sites are occupied __ per unit cell. b) How many si atoms per unit cell (or within unit cell) ___ (justify your answer below) c) What is the coordination of the Si atoms in the lattice d) If all the foc atoms in the structure are substituted by Ge what would the composition be of the resultant material (show work) e) Which type of bonds do you expect in this material (Ge-Ge, Si-Ge, Si-Si ?) please explain.

Answer 1

In an fcc comit cell 8 Cooner atoms have constribution / each. Because of one atom is shar red by eight mit Cell. FCC And face aboms have contribution / each as it shared by two to mit cell. so total contribution 681 +8xYg (face) commer) totalatom. 3+1 24. In case of Combic system the teha hedral sites is twice that of total atoms, and octahedral a "sama as total atoms . Tetrahedral sites a 2x428 tehra hedral void. Octahedral sites 2 4 . Octahedral