Question

5) For the following structure, give the Bravais lattice and determine the lattice parameters, the packing factor and the theoretical density. If the unit cell is smaller than that shown, sketch the smaller unit cell. Show your work. Open circles represent A atoms: ra = 1.5 Å, AWA = 100 g/mole Filled circles represent B atoms: rb = 1.0 Å, AWB = 40 g/mole Cross-hatched (or gray) circles represent: C atoms: rc = 1.3 Å, AWB = 60 g/mole Na = 6.02 x 1023 atoms/mole Bravais lattice: Lattice parameters: Packing Factor: Density:

Answer 1

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Bravais Lattice: FCC - Face Centered Cubic Lattice Paramete: a = 21a VA = 4,242 Aº for FCC only Packing Factor For FCC; P.F = atom. Aunit cell = * ( /4] Volume /unit cell a3 = 0.74 a3XNA Density 7 - no.of atoms per unit cell d = ZxM d-density (gm Ic mat) M- Molar mass in gro/mole ma - edge length in cm (4.242x 16) *(6-02 x103) Na - Avagadro constant in d = 8.704 gm Icma3 = 4x 100 per mol The given figure itself is smaller unit cell as unit cell is determined by one Kind of atom either A or B atoms (A atoms in this case).

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