I am having an internal struggle with this. I have samples which are cubic and yield high quality diffraction patterns out to 120 °2Θ using a Cu-based Lab XRD instrument with good resolution. When analyzing synchrotron data I see the same trend in lattice parameters between samples but with smaller magnitudes. Which lattice parameters are a closer representation of the actual lattice parameter?
With sync you have inherently higher resolution, and more observed peaks, but you have a more limited range of °2Θ coverage and the wavelength actually used may not be accurately defined.
With Lab XRD we can collect a full range of °2Θ with a known wavelength.
So educate me; sync or lab XRD for lattice parameters?
I think the answer cannot be given in a straightforward manner. X-ray diffraction using lab equipment in fact offers a large 2-theta range, but using synchrotron radiation, one may easily gain similar q-space by using higher photon energies without loosing resolution, so this is not an argument in may mind.
In fact it is true that doing X-ray diffraction at a synchrotron, the actual energy needs to be thoroughly checked, due to small angular variations of the monochromator the energy may easily change by some eV with related changes of the Bragg angles. However, a variation of the energy should affect all Bragg peaks in the same way, and if all samples are measured under identical conditions, then the trend should be the same, compared to X-ray tube driven lab. experiments.
I think the answer is more related to the detector equipment used. Especially in synchrotron experiments, in most cases 2D-area detectors are used, and the flat panel of those detectors have to be carefully converted to a circle, on which the Bragg peaks are measured with a point detector using lab equipment - thereby the observed differences may easily result when the two setups are compared.
So I feel that - if very precise results are to be achieved - huge efforts and careful data treatment, sample alignment, etc are necessary.
Thus, I would propose to check proper aligment, calibration and conversion. Good luck in re-analyzing your data :-), Dirk
A better values for lattice parameter can be obtained from the available higher diffraction angle peakes since the higher angles doesn't contain effects of the refraction and they are with a higher angle resolution which gives a more sharper peaks to give more accurate values in measurements
I think the answer cannot be given in a straightforward manner. X-ray diffraction using lab equipment in fact offers a large 2-theta range, but using synchrotron radiation, one may easily gain similar q-space by using higher photon energies without loosing resolution, so this is not an argument in may mind.
In fact it is true that doing X-ray diffraction at a synchrotron, the actual energy needs to be thoroughly checked, due to small angular variations of the monochromator the energy may easily change by some eV with related changes of the Bragg angles. However, a variation of the energy should affect all Bragg peaks in the same way, and if all samples are measured under identical conditions, then the trend should be the same, compared to X-ray tube driven lab. experiments.
I think the answer is more related to the detector equipment used. Especially in synchrotron experiments, in most cases 2D-area detectors are used, and the flat panel of those detectors have to be carefully converted to a circle, on which the Bragg peaks are measured with a point detector using lab equipment - thereby the observed differences may easily result when the two setups are compared.
So I feel that - if very precise results are to be achieved - huge efforts and careful data treatment, sample alignment, etc are necessary.
Thus, I would propose to check proper aligment, calibration and conversion. Good luck in re-analyzing your data :-), Dirk
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