Help needed with Crystal structure

In summary, Adam found that there are twelve nearest neighbours to an atom in the fcc lattice, and that the spacing is 2.856 A.
  • #1
smashing
6
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Hi all I am new here but i have a major question, iv been told by people that this question is easy but I am just going around in circles with it and i was wondering if you could help.

here is the questionAluminium cystallises in the fcc structure with a single atom basis. the lattice constant is 4.04 A and the atomic weight of aluminium is 27 a.m.u

a) deduce the number of nearest, next nearest and third nearest neighbour atoms and their separations.now i understand that the lattice constant corresponds to the length of each side of the cube. My textbook says that the fcc lattice has one atom at each corner and one in the centre of each face of the cube making for a total of 4 atoms in the cube. Now can the spacing from one corner atom to a face centred atom be found using simple Pythagoras meaning that the separation to the nearest atom would be sqrt(2.02^2 + 2.02^2)?? or am i visualising all this wrongany help on what this structure actually looks like would be really helpfull as i find it hard to visualise.thanks
adam
 
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  • #2
hi i got the answer in the end :D
 
  • #3
Hello Adam!

A Very Good Question.
And, yes it is a bit difficult to visualise this fcc structure. Before understanding how I solved this, you are required to get the following file from which I give reference for further clarification. You will get visualisations here.

http://www.4shared.com/file/62877111/ac7097ff/introduction_to_solid_state_IIT.html

This structure is also known as ccp structure which is formed due to ABCABC_ _ _ pattern of stacking of atoms. (page 4----questions 3 and 4)

The number of first nearest atoms is 12. (page 5----question 7)

The spacing will be just 2r = (sqrt 2 )*4.04/ 2 = 2.856 A (page 7----question 15)
Where 4.04 A is the edge length,a, of the unit cell.

I am sure upto this. But the validity of the following must be checked.

The number of second nearest = 6 (not sure)
The distance between second nearest = edge length = a = 4.04 A (I am sure)
 
  • #4
hi,
i managed to get the same answers as you :D thank you for the link i will be reading through that file :D thanks for the help
 
  • #5
Could you please post the answer that you got on the forum?
 

1. What is a crystal structure?

A crystal structure is the arrangement of atoms, molecules, or ions in a crystal. It is the three-dimensional pattern of a crystal lattice, which determines the physical properties of a crystal.

2. Why is understanding crystal structure important?

Understanding crystal structure is important because it helps scientists and engineers understand the physical and chemical properties of materials. This knowledge is crucial for developing new materials and improving existing ones for various applications, such as in electronics, medicine, and construction.

3. How is crystal structure determined?

Crystal structure is determined through various techniques, including X-ray diffraction, electron diffraction, and neutron diffraction. These techniques allow scientists to analyze the arrangement of atoms in a crystal and determine its crystal structure.

4. What factors can affect crystal structure?

Crystal structure can be affected by factors such as temperature, pressure, and impurities. These factors can cause changes in the arrangement of atoms in a crystal, resulting in different crystal structures and properties.

5. Can crystal structure be changed?

Yes, crystal structure can be changed through processes such as heating, cooling, or applying pressure. These changes can result in different crystal structures with different properties, making it possible to tailor materials for specific uses.

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