dear experts,
in the attachment you will find pictures of two materials powder. first picture is wollastonite, where most of the peaks have a V shape in the tip and also the noise of background is high. the second picture is for MgO, there is a kind of zigzag shape in the peak, this is very bad when we do quantitative analysis witch effect the broadening of the peaks. I hope I can have solution for these problems. the lab device is shimadzo 6000, the measurement conditions are:
cu target, divergence slit 1 deg, scatter 1 deg, receiving 0.3 mm, we used two scan mode in MgO we used fixed scan ( 0.5 preset time (s)),and in wollastonite we used continuous scan 2 deg/min.
best regards
Your first diffractogram suffers from noise (to my opinion); noise is also present at peak tips. Please significantly increase measurement time and you will most probably get nice peak tip profiles.
With respect to the MgO sample the impression of Gert is right. Is this profile repeatable? How does the MgO look like when also measured by constant scan speed as for the wollastonite case?
With respect to increase peak resolution you have to go two ways in lowering the net angular divergence:
a) reduce slit width(s), b) reduce sample length.
I must admit, that both actions have to be paid by loss in x-ray flux or increase of measurement time. But that is law in optics.
To me the second curve looks more like at least two peaks slightly shifted to each other. This commonly happens in case of pseudosymmetry (lower symmetry with pseudo-equivalent hkl), i.e. symmetry reduction and lattice distortion.
Your first diffractogram suffers from noise (to my opinion); noise is also present at peak tips. Please significantly increase measurement time and you will most probably get nice peak tip profiles.
With respect to the MgO sample the impression of Gert is right. Is this profile repeatable? How does the MgO look like when also measured by constant scan speed as for the wollastonite case?
With respect to increase peak resolution you have to go two ways in lowering the net angular divergence:
a) reduce slit width(s), b) reduce sample length.
I must admit, that both actions have to be paid by loss in x-ray flux or increase of measurement time. But that is law in optics.
Hi, maybe you can try to increase the mA for the instrument. And reduce the step size of scanning, say 0.01 degree per step. Sometimes it helps to get better resolution of diffractogram.
Dear Fareezex,
increase in mA increases x-ray flux and reduces noise and thus will increase signal to noise ratio (the peaks will look more pretty); but peak resolution is not affected.
This also holds for increase in step size; peaks will appear smaller in width due to lower number of data points across their widths; but resolution/FWHM (in 2theta) is not affected. Peak resolution is given by sample properties such as crystallite size and stress/strain therein and angular divergence of involved x-ray beams of your x-ray set up.
The sample is as it is. So the angular divergence has to be improved (decreased) in any way to improve peak resolution.
Hi,
Peak width has a correlation to the degree of crystallinity of your sample. In addition to all other suggestions by others, I would look at the your sample. Mosaicity of the crsytal is a good indicator that tells you how good the crystal is. If I remember correctly, Wollatonite is known to be polysynthetic twinned. That means that, there may be more than one repeating block in your crystal that may be alternating irregularly making the whole crystal looks like a twinned. You cannot avoid this type of twinning even in powder XRD. Most probably reason for this to happen is having some sort of pseudosymmetry in the structure/structural packing. You may find more details in Order-Disorder theory by Dornburger-Schiff back in 1950s.
Rangana
It may be that the crystal quality (grain size distribution) of your two samples is vastly different. For XPD it is optimal to have a grain size distribution of say 0.5 to 1-ish microns. Large grains (> ~ a few microns) can generate intense single-crystal-like reflections that need to be masked out before 2D integration of XRD images and nano-sized grains (if predominate) will also lead to highly broadened Bragg peaks.
Lastly, assuming grain size is not an issue nor the points raised above, one can increase the sample-to-detector distance to help better resolve Bragg peaks. Unfortunately, your in-house x-ray system makes it difficult to change the XRD source energy like we do at some synchrotron-based beamlines.
It may be that your apparently high signal background is due to Compton scattering, which is surprising for an in-house XRD source. One can use multi-channel slits to significantly reduce background; however, the data collection time will increase and the cost in time and capital resources may not be worth the investment. A final thought - you may have a significant amt. of nano-sized material mixed with larger grain material. The nano-sized crystals may give the appearance of a high signal or diffuse scattering background in addition to your Bragg peaks.
Good Luck.
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