Bragg's Law and lattice spacing problem - boards.ie

27-06-2011, 20:52   #1
El Siglo
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Bragg's Law and lattice spacing problem

I'm currently starting work using XRD but there's something driving me mad, I came upon this website explaining how they worked out the lattice spacing for a specimen. However, every time I try and do it I keep getting a wrong answer for d in comparison to what the authors got. Would anyone here know what they managed to do?

Here's the example:
Quote:
 C. This is one of the X-ray peaks. It happens to be the one with the smallest angle which I measured as 23.04 degrees. Solving Bragg's Law (with n=1 and wavelength=1.54 ang) we find that 23.04 degrees 2-theta corresponds to a d-spacing of 3.86 angstrom.
Here's what I've done:

2d(sinθ)=λ

2d(sin 23.04)=1.54
2d(0.391)=1.54
0.782d=1.54
d=1.54/0.782
d=1.969

I'm not sure where I've gone wrong? Any help would be much appreciated!

27-06-2011, 23:41   #2
Turtwig
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Quote:
 Originally Posted by El Siglo I'm currently starting work using XRD but there's something driving me mad, I came upon this website explaining how they worked out the lattice spacing for a specimen. However, every time I try and do it I keep getting a wrong answer for d in comparison to what the authors got. Would anyone here know what they managed to do? Here's the example: Here's what I've done: 2d(sinθ)=λ 2d(sin 23.04)=1.54 2d(0.391)=1.54 0.782d=1.54 d=1.54/0.782 d=1.969 I'm not sure where I've gone wrong? Any help would be much appreciated!
I think it's just their wording that's confusing you.
Quote:
 For practical reasons the diffractometer measures an angle twice that of the theta angle. Not surprisingly, we call the measured angle '2-theta'.
2θ = 23.04. θ = 11.52. Plug that in and you should get their values.

Last edited by Turtwig; 27-06-2011 at 23:47.

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28-06-2011, 08:09   #3
El Siglo
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Quote:
Originally Posted by Malty_T
Quote:
 Originally Posted by El Siglo I'm currently starting work using XRD but there's something driving me mad, I came upon this website explaining how they worked out the lattice spacing for a specimen. However, every time I try and do it I keep getting a wrong answer for d in comparison to what the authors got. Would anyone here know what they managed to do? Here's the example: Here's what I've done: 2d(sinÎ¸)=Î» 2d(sin 23.04)=1.54 2d(0.391)=1.54 0.782d=1.54 d=1.54/0.782 d=1.969 I'm not sure where I've gone wrong? Any help would be much appreciated!
I think it's just their wording that's confusing you.
Quote:
 For practical reasons the diffractometer measures an angle twice that of the theta angle. Not surprisingly, we call the measured angle '2-theta'.
2Î¸ = 23.04. Î¸ = 11.52. Plug that in and you should get their values.

I just did it there and it came out correct, I feel like such an idiot! Thanks a million!