I Identification of index of Bragg peaks for NaCl

[Hello890]

In my x-ray crystallography data for a single crystal of NaCl using x-rays generated by Cu k alpha (154 pm), there are three peaks identified at angles of 14.155, 31.475 and 53.5 degrees.
According to http://www.nada.kth.se/~fabo02/solid/xray.pdf, these peaks must correspond to only even values of h, k and l (as there is quite a lot of background noise)
How can I then identify which peak corresponds to which layers?

 

[Lord Jestocost]

Why not following the “recipes” given in http://www.nada.kth.se/~fabo02/solid/xray.pdf. As you are using Cu K-alpha X-ray radiation, you can use equation (8) to determine Sqrt(h² + k² + l²) for the three measured angles in order to roughly check whether there is something in common. As you are measuring on a NaCl single crystal, the measured peaks must belong to a certain set of planes.

 

[Hello890]

Why not following the “recipes” given in http://www.nada.kth.se/~fabo02/solid/xray.pdf. As you are using Cu K-alpha X-ray radiation, you can use equation (8) to determine Sqrt(h² + k² + l²) for the three measured angles in order to roughly check whether there is something in common. As you are measuring on a NaCl single crystal, the measured peaks must belong to a certain set of planes.

Many thanks for your reply. I have find the values of h, k, l as being closest to (2, 0, 0), (4, 0, 0), (6, 0, 0) as my parallel planes. Could I use to justify that the structure of the crystal is face-centered cubic?

 

[Lord Jestocost]

Could I use to justify that the structure of the crystal is face-centered cubic?

I don’t think so. Appropriate aligned crystals with other crystal structures could give rise to a peak pattern which could be assigned in the same way.

 

[Hello890]

I don’t think so. Appropriate aligned crystals with other crystal structures could give rise to a peak pattern which could be assigned in the same way.

Can I safely say that the planes identified are indeed the correct ones, even though the plane of the cut of the crystal is unknown? Also, can I use the method in http://pd.chem.ucl.ac.uk/pdnn/diff2/structf.htm to calculate the relative intensities, will the formula work for single crystals as well?

 

[Lord Jestocost]

Can I safely say that the planes identified are indeed the correct ones, even though the plane of the cut of the crystal is unknown?

As you are measuring on a NaCl single crystal, the planes identified seem to be the correct ones. I am, however, surprised about the measured theta values of 14.155, 31.475 and 53.5 degrees which indicate a severe misalignment of your diffractometer. The correct ones should be 15.85° (200), 33.11° (400) and 55.02° (600) when assuming a lattice parameter of 0.5640 nm.

 

[Hello890]

As you are measuring on a NaCl single crystal, the planes identified seem to be the correct ones. I am, however, surprised about the measured theta values of 14.155, 31.475 and 53.5 degrees which indicate a severe misalignment of your diffractometer. The correct ones should be 15.85° (200), 33.11° (400) and 55.02° (600) when assuming a lattice parameter of 0.5640 nm.

Yes, unfortunately the equipment we were given was not well aligned and so an offset had to be taken into account. Should I perhaps identify the planes using the ratio of the sin^2(measured angle 1) / sin^2(measured angle 2 - of next peak) = (h1^2 + k1^2 + l1^2)/ n^2(h2^2 + k2^2 + l2^2)? Would this work?

 

[Lord Jestocost]

Would this work?

The best way would be to correct the peak positions to a first approximation by applying a simple zero point shift.