'Scan angles' in XRD are the diffraction angles (theta) or scatter angles (2theta) which have been used for taking and presenting the XRD pattern.

The XRD pattern acquisition is usually done by 'step and shoot' mode; i.e.

repeatedly by

a) stepping forward a preset angle delta_theta of the goinometer

followed by

b) acquisition the x-ray photon counts in a preset time interval at that angular position of the goinometer

and so forth ...

'Important scan angles' is the region of theta (2theta) angles of the XRD pattern in which your peaks show up. In most of the cases it is sufficient to start around 10 or even around 20° in 2theta.

This does not mean that in general the low 2theta region does not contain structural informations. For amorphous systems this low angle region bears a lot of informations too. 'Small angle x-ray scattering' (SAXS) is here the buzz word....

Best regards

G.M.

In addition to the answer given by Gerhard, I would suggest to plot data not as a function of the angle, but as a function of the scattering vector Q. The scattering angle depends on the wavelength of the scattering radiation. So if you use a Cu anti-cathode you will find the same diffraction line at a different angle (theta) when you use (for example) a Fe anti-cathode because of the different wavelength (lambda). The angle is thus dependent on an instrumental parameter. Conversely, the scattering vector Q [4pi*(sin_theta)/lambda] is truly dependent only on the structural properties of the inspected sample. This means that you will find the same diffraction line at the same Q-values, independently on the wavelength that you use.

The angular value of 2 theta for the start of the scan depends a lot on the material being measured. For example, clay minerals, zeolites, etc. have significant diffraction lines at very low angles of 2 theta. Without knowledge of the first line, the evaluation is not reliable, sometimes even impossible. For example, the clay mineral corrensite has d(001) line at about 29-30 Angstr.

Dear sir, what does mean of scan angle here.? It means important angles of the desire material of which the peaks is present.?

I don't really understand the question. It is necessary to set the angle value on the device for the beginning, end of measurement, measurement step and time per step. In this section there are several (for cubic materials) or even several hundred diffraction maxima, i.e. peaks (phases with low symmetry). For identification, intense lines are especially important, and rather at low angles. Common practice in our laboratory is to measure in the angular range of 5 to 80o 2 theta, but there are of course exceptions.

Dear Yaseen Muhammad ,

the 'scan angle' is the theta angle, which is used in the experiment to acquire the XRD pattern as a function of the goniometer settings theta, as Dalibor Matýsek already said.

The display is done in the XRD community by the 2theta scale.

Dear Alberto Martinelli , you are right; the theta (or better 2theta) scale should be replaced by the magnitude of the scattering vector Q [4pi*(sin_theta)/lambda], also known as the momentum transfer vector.

This scale is independent on the wavelength, as you said, and is mainly used by the scatter people. It should be used by the XRD people too...

But one has to take care when using the Q scale. Often the conversion Q=(sin_theta)/lambda is used with the factor 4*pi omitted. So one has to take care when having a look at a scatter pattern presented with a Q axis...

Best regards

G.M.

@Gerhard Martens you're right! I forgot to mention the slight difference in the reciprocal lattice vectors definition assumed by the crystallography and solid state physic communties.

For this, please check the latest preprint article at DOI: 10.13140/RG.2.2.27720.65287/3