0
$\begingroup$

About the assignment of $\{hkl\}$ indexes to a set of diffraction data I usually find this kind of statements but never too much detailed:

  1. a diffractogram of a powder sample can be indexed automatically, but in general we start hypothesizing the maximum symmetry (cubic) and so on, with increasing difficulty. The procedure and some simple 'manual' examples are clear to me, the maths seems simple. This way can lead in unlucky cases to ambiguous conclusions.

  2. indexing the diffraction pattern of a single crystal apparently relies on a complicated black box method, but is quickly and more accurate than the previous one.

What is the physical cause of this two differences (mathematical difficulty for the single crystal and poorer success for powder)? Why the maths and the experimental part involved are different?

Improve this question
$\endgroup$
3
  • 2
    $\begingroup$ Why, that's simple: in powder diffraction, each reflection has only one $\theta$ angle with rather simple connection to $\{hkl\}$. In single crystal diffraction, each reflection has three angles, hence more info, hence greater accuracy, but at the cost of more complex processing. $\endgroup$
    – Ivan Neretin
    Commented Aug 31 at 6:59
  • 4
    $\begingroup$ Diffraction (elastic scattering) is not a spectroscopic (anelastic scattering) technique. Avoid using meaningless terms such as "diffraction spectra" or "powder spectrum". You have a "diffraction pattern" or a "diffraction profile", not a spectrum. $\endgroup$
    – gryphys
    Commented Sep 3 at 5:37
  • $\begingroup$ PXRD frequently is not in the comfortable situation of a high ratio of number of observations (i.e., diffraction peaks) over parameters to refine seen in scXRD. Setup, sample-detector distance, wavelength, (reciprocal) unit cell, etc. contribute here. scXRD on the other hand (typically) reports lattice constants for the analysis of one crystal only per model. Is this one representative for the sample? PXRD is better on this one (i.e., to check phase purity). One equally can disable refinement of (a,b,c,...) during the data reduction of scXRD, or use (a,b,c,...) obtained by PXRD. $\endgroup$
    – Buttonwood
    Commented Sep 3 at 15:37

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.