Dear TOPAS-experts

I am trying to estimate the size of some antiphase domains using synchrotron data from ESRF, and although I get reasonable values in my attempt I do not feel too confident about the physical meaning, and would like to get some feedback from more experienced users/crystallographers. I have cation ordering in my material but the ordering is believed to only arise in smaller domains, separated by antiphase boundaries. All supercell peaks arising from the cation ordering (hkl-values with mixed even/uneven parity) are broader than the characteristic peaks that are present in both the ordered and disordered material. I looked into the topas wiki and found this: https://topas.awh.durham.ac.uk/doku.php?id=anisotropic_broadening

As opposed to the example above, the peak broadening arise in all three dimensions and I thus expanded the equation from only including C_star to also A_star and B_star (see below). However, as also the characteristic peaks have some (not much) lorentzian broadening, I was tempted to add a CS_L-term. However, I have restrained from adding this to the refinement, as this would affect both supercell and subcell peaks and I am thinking this might give me incorrect values for the antiphase domain size (Xi_AP). In stead I add a separate lor_fwhm term to the subcell peaks, using the same formula - only refining the domain size as Xi_sub. The lor_fwhm below is thus the only lorentzian contribution I add to account for the broadening, in addition to some gaussian strain-component. Visually it looks okay, but I am still not 100% sure I am going about this the correct way.

Furthermore - will the number I get from this have the same unit as the wavelength (Å)?

Are there anything else I should be aware of before correlating this with the estimated domain size? The values I get are typically 40-200 for the supercell peaks, whereas >1000 for the characteristic peaks, varying a lot from sample to sample.

lor_fwhm =

  IF (Mod(H,2)+Mod(K,2)+Mod(L,2)==1) THEN
  	   (A_star * (H^2)^0.5 +B_star * (K^2)^0.5 +C_star * (L^2)^0.5 )*D_spacing Lam / (Pi * Xi_AP Cos(Th)) Rad 
  ELSE IF (Mod(H,2)+Mod(K,2)+Mod(L,2)==2) THEN
  	   (A_star * (H^2)^0.5 +B_star * (K^2)^0.5 +C_star * (L^2)^0.5 )*D_spacing Lam / (Pi * Xi_AP Cos(Th)) Rad
  ELSE
    (A_star * (H^2)^0.5 +B_star * (K^2)^0.5 +C_star * (L^2)^0.5 )*D_spacing Lam / (Pi * Xi_sub Cos(Th)) Rad
  ENDIF
  ENDIF
  ;

PS: The material is a cubic spinel.

Best regards,
Halvor H. Hval