Antiphase boundary (APB) in topas refinement

Jamal

Hi everyone,

A relatively-less-experienced Topas user her. Running a keyword search unfortunately didn't given any results, so I had to start this not knowing if this has been discussed already.

I want to add planar defects to my refinement of transition aluminas (cationic-sublattice defective spinel and lower symmetries) but I unfortunately don’t know how it’s implemented in Topas (V7). More specifically, I need to use antiphase boundaries (ABP) and twinning of domains.

I’m using the right model for my gamma-alumina and by fitting the Al occupancy I get a fit which is not very bad given the quality of the data, but I need to consider ABP in the refinement because visually hkl-dependent ABP effect is present.

Are planar defects treated explicitly in Topas? If yes, how?

I’m already using ‘LVol_FWHM_CS_G_L’ for CS and ‘e0_from_Strain’ for strain which also randomly swings between the extremes inversely if both are refined simultaneously.

So, I have site occupancy, CS and strain. Is there anything I’m missing if I’m dealing with something which potentially has planar defects?

Thank you in advance for your help!

Best regards,

Jamal

johnsoevans

You can do stacking fault type-refinements as at the link below. Will this do what you want?

https://topas.webspace.durham.ac.uk/tutorial_stacking_faults/

Jamal

johnsoevans Thank you for sharing this, I'm reading the materials you shared. For the macrocell in the input file, do I need to make sure it stays within the actual crystallite size?

johnsoevans

No. You can have an unrealistically large overall stack in a similar way to having an infinite crystal as your starting point in normal refinements. You can think of different local regions of your stack (which differ due to different faults created by your probabilities) as representing individual small domains of a real sample.

Of course if you have (e.g.) 10 nm crystallites you could never see broadening effects due to stacking faults that are e.g. 40 nm apart - their effects would be swamped by the size broadening. Similarly you won't be sensitive to broadening from very long range faults if you have a low instrumental resolution.

Jamal

johnsoevans Thank you, that was quite useful. I might get back to ask for help as I make progress.