# How can I solve a non-cubic crystal structure?

Say I want to solve the crystal structure of barium sulfate, and I want to not only determine crystal type and the lattice parameter, but also the orientation of the oxygen atoms on the sulfate anion. How do I proceed? All I have is the powder X-ray diffractogram (i.e. intensity vs $2\theta$ for the compound).

I don't want to use any existing software as this is more about learning how crystal structures are solved. I have looked at books and they seem to be incredibly difficult to follow.

• This is rather a big question, the only way is to work through some examples, there are several in McKie & McKie ' Essentials of Crystallography' (publ Blackwell Scientific), chapter 7 is all about power photographs and their analysis. – porphyrin Mar 11 '17 at 9:06
• Thank you. I will go through the book suggested and get back on this comment thread. – gluco Mar 11 '17 at 15:26
• This is ...probably possible - in some cases. I sat 2 years interpreting XRD data with EVA and Rietveld curve-fitting software (TOPAS) - and I am certain I would not be able to do so. You would have to be very experienced, because interpretation of a crystallogram, if you do not know the rotation nor lattice parameters at all, is tricky. You would have to be able to - in your mind - picture the different planes and their diffraction peaks - as you rotate the crystal - and recognize them in the diagram. If anyone could do that, and were female, I would very politely ask her to have my babies. – Stian Yttervik May 11 '17 at 13:50

The lattice constants and the symmetry of the lattice determine the position of the diffraction peaks observed along the $2\theta$-scale. The intensity of the diffracton peaks, leaving out increase by accidental or systematic superposition of them, is due to the arrangement within the asymmetric unit, i.e. the motif which -- after application of the symmetry operators (centres of inversion, proper axes, rotoinversion axes, glide planes, mirror planes) -- builds the unit cell.