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Bragg's Law and lattice spacing problem

  • 27-06-2011 8:52pm
    #1
    El Siglo
    Registered Users, Registered Users 2 Posts: 3,803 ✭✭✭


    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:
    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!:D


Comments

  • #2
    Turtwig
    Registered Users, Registered Users 2 Posts: 26,578 ✭✭✭✭Turtwig


    El Siglo wrote: »
    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!:D

    I think it's just their wording that's confusing you.
    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.:)


  • #3
    El Siglo
    Registered Users, Registered Users 2 Posts: 3,803 ✭✭✭El Siglo


    Malty_T wrote: »
    El Siglo wrote: »
    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!:D

    I think it's just their wording that's confusing you.
    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.:)


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


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