Why is the volume of FCC and BCC different in reciprocal space?

In summary, the BCC structure has a simple cubic lattice with one basis in the center, resulting in a total of 2 atoms per unit cell and a primitive unit cell volume of 1/2*a^3. In reciprocal space, the BCC structure becomes an FCC structure with a simple cubic lattice of length 2pi/a and a total of 4 atoms. The total volume in reciprocal space is then 4*(2pi/a)^3, not 1/4*(2pi/a)^3. Similarly, the FCC structure has 3 basis in real space, with a total of 4 atoms per unit cell and a primitive unit cell volume of 1/4*a^3. In reciprocal space, the FCC
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Taken from http://dao.mit.edu/8.231/BZandRL.pdf

BCC

In real space, it has a simple cubic lattice with one basis in the centre. Total number of atoms per unit cell = 2. Volume of primitive unit cell is then ##\frac{1}{2}a^3##.

In reciprocal space, BCC becomes an FCC structure. It has a simple cubic lattice of length ##\frac{2\pi}{a}## with 4 atoms in total. Why is the total volume then ##4 \left(\frac{2\pi}{a}\right)^3## and not ##\frac{1}{4}\left(\frac{2\pi}{a}\right)^3##?
FCC
In real space, it has a simple cubic lattic with 3 basis. Total number of atoms per unit cell = 4. Volume of primitive unit cell is then ##\frac{1}{4}a^3##.

In reciprocal space, FCC becomes a BCC structure. It has a simple cubic lattice of length ##\frac{2\pi}{a}## with 2 atoms in total. Why is the total volume then ##2 \left(\frac{2\pi}{a}\right)^3## and not ##\frac{1}{2}\left(\frac{2\pi}{a}\right)^3##?
 
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  • #2
What is the the magnitude of the unit vectors of the reciprocal lattice? I don't think the size of the reciprocal cube for BCC is 2pi/a.
 

1. What is the difference between BCC and FCC structures?

BCC (Body-Centered Cubic) and FCC (Face-Centered Cubic) are two types of crystal structures commonly found in metals. The main difference between them is the arrangement of atoms within the unit cell. In BCC, there is one atom at each corner of the cube and one atom in the center, whereas in FCC, there is one atom at each corner of the cube and one atom on each face of the cube.

2. How does the volume of a BCC/FCC structure compare to other crystal structures?

The volume of a BCC/FCC structure is typically larger than other crystal structures such as HCP (Hexagonal Close-Packed) or SC (Simple Cubic). This is because BCC and FCC structures have more atoms per unit cell, resulting in a higher density and larger volume.

3. What is the formula for calculating the volume of a BCC/FCC unit cell?

The formula for calculating the volume of a BCC/FCC unit cell is V = a^3, where "a" is the length of the edge of the unit cell. This is because in BCC/FCC structures, the unit cell is a cube, and all edges have the same length.

4. How does the volume of a BCC/FCC structure change with temperature?

As temperature increases, the volume of a BCC/FCC structure also increases. This is because the thermal energy causes the atoms to vibrate and take up more space, resulting in a larger volume. This effect is known as thermal expansion.

5. Can the volume of a BCC/FCC structure be measured experimentally?

Yes, the volume of a BCC/FCC structure can be measured experimentally through various techniques such as X-ray diffraction, neutron diffraction, or electron microscopy. These methods allow for the determination of the unit cell dimensions, and therefore, the volume can be calculated using the formula V = a^3.

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