Tried XRD yet?

Dear Ravi,

this phase is forming at an interface as a layer with less than two microns in thickness. Thus, conventional XRD seems not really to be an option.We prepared a FIB lamella for TEM analysis. At this lamella we only find a few grains. On the other hand our double tilt holder posses a limitied tilting range. I only have access to a limited number of zone axes, that do not show the outstanding five-fold symmetry, but strange ones.

My hope is that someone of the quasicrystal community can judge quickly and easily from the posted pattern just based on his/her experience...

• Please describe your sample better. 
• " interface as a layer with less than two microns in thickness". Thick enough for XRD in my opinion. Transmission Laue would be an option :-)
• "conventional XRD seems not really to be an option". Sure! It is only a choice. I suggest a myriad of other modern XRD techniques tried and tested for nearly a century using photographic film. These days one has the added advantage of 2D real time XRD imaging devices as well.
• "We prepared a FIB lamella for TEM analysis. At this lamella we only find a few grains." - Sample prep is an inherent challenge with most Electron Microscopy as well as AFM etc.  
• What XRD equipment do you have access to?
• XRD is NDE and may be used "in situ"!
• "My hope is that someone of the quasicrystal community can judge quickly and easily from the posted pattern just based on his/her experience..." That would be an excellent learning experience for me :-)
• So, why have you not considered XRD before FIB/TEM? Wouldn't XRD make more sense prior to laborious sample prep? Are these crystals stable at room temperature and ambient conditions? Just curious as to the thought process :-)

https://www.flickr.com/photos/85210325@N04/10515372183/in/album-72157645018820696/

It might be special boundary as well,  CSL (coincidence site lattice).

Plz refere this, http://scripts.iucr.org/cgi-bin/paper?s056773947400043x

Dear Chandrasekhar,

many thanks for your suggestion, but I checked carefully that there is no overlap to adjacent grains during acquisition of the SADP. Thus a boundary or better an orientation relationship in terms of two overlapping diffraction pattern is not displayed in the SADP. 

Dear Ravi,

thanks a lot for your stimulating ideas. However the circumstances are a little bit more complex...

• First of all, this result is from industrial research: I am not allowed to post further details of neither fabrication nor application – it’s a pity.

However the phase observed is stable at room temperature, but I think far from thermodynamic equilibrium.

• Currently we do not have such an advanced XRD setup (like 2D imaging or in-situ stage) and additionally I am not allowed to forward the sample to other departments.
• The layer is just a part of a big ensemble of several layers that are above and underneath. The layer roughness is in the same order of magnitude as its thickness. Furthermore the layer itself is not a single crystal. It is polycrystalline and consists of micrometer sized grains. Over all this makes a preparation in terms of separation of the phase for XRD in transmission very challenging.

I think this SAED pattern is for supersaturate solid solution structure. Heterogeneous atoms (e.g. Ni) clustered ordering on some specific crystal plane (e.g. {001}) may bringabout the period  weaker reflections pattern. Moreover,The characteristic (that is the region with this special pattern is only 2 microns) fit well with the the formation mechanism of supersaturate solid solution structure. Hope can help you.

Dear Zhexu,

good point, my first idea was exactly the same, that the weaker reflections were caused by a super structure - like in our last joint publication ;-).

But considering the symmetry of the weaker reflections, they do not display a centrosymmetric dependency. From my understanding a zone axis pattern should always be centrosymmetric. This was the point when the things became strange…

Cheers

Martin

It might be that you are not in a zone axis and two Laue zones are interfering with each other. The zero order Laue zone(strong spots) and the first order Laue zone (weaker due to higher excitation error s) then have a translation of half the spacing if you have instead of m `2` symmetry. By tilting the specimen the weak reflections should go away and show inhomogeneous intensity distribution over the Field of view till you reach a zone axis in which they will show up as a round circle around the zero order Laue zone.

Double diffraction is another way of explaining the pattern. You have the two identical crystals on top of each other and every diffracted beam of the upper crystal can act as a primary beam to make a complete diffraction pattern with shifted symmetry point. In this case the crystals are rotated to each other around the beam direction. If you know the central beam you can determine the rotation angle of the two crystals with the same structure. Which one of the beams is the central beam here?

Thanks for your stimulating suggestions.

I used the Kikuchi-pattern to align the crystals orientation. Thus, the orientation is pretty close to the zone axis and should display only ZOLZ reflections (see symmetry of the SADP appended).

Double diffraction seems to be an opportunity. The probed position at the FIB lamella is relatively thick.

I marked the positon of the central spot in the DP (arrow). Plese tell me how to deduce a rotation (~relationship)?

Fiedels law is broken with this central beam. No double diffraction is possible since +-g vectors are not present at the same time in opposite directions. Is the sample strongly magnetic and two different magnetic domains in the FOV cause a shift in the diffraction pattern of one domain compared to the other? Did you try dark field imaging with one of the spots to see if a particular area is flashing up in the DF image or the entire area is bright? Maybe you have to tilt away form the zone axis to bring more intensity in the used spot. you need a small objective aperture for this exercise and a LaB6 tool is giving you more current to get a decent intensity.

Since the pattern is not centrosymmetric Friedels law is broken.

As I know and I also checked quickly the literature, there is no ferromagnetism of ZrTiNi compounds reported.

I will try dark field (CDF) to highlight several features – good point.

We have an LaB6 machine equipped with small objective apertures - should work.

Many thanks

Martin