Hi Xiujun & Tim,
while I am not familiar with the texture analysis offered in Topas, I can
offer a few hopefully useful hints.
- The texture index is a number that is 1 for a perfectly random sample and
infinity for a single crystal. A weak texture would have an index between say
1 and 1.5, a moderate texture between say 1.5 and 3. Above that one can say
the sample has a strong texture. I am not aware of a standard for this, so
these numbers might be somewhat biased with my personal judgement.
- The texture index condenses the whole ODF into a single number, so it's
value is fairly limited.
- Before you attempt to do combined texture and structure refinements, you
should establish that your pole figure coverage in your given instrument
setup is sufficient. Any texture analysis will refine to some numbers, but if
there is not enough pole figure coverage they will be meaningless, flawing
your structure analysis.
- If you don't use an image plate, you will most certainly not have enough
coverage from a single sample orientation. Even with an image plate, you
might need multiple sample orientations.
- To establish whether the texture analysis works, you could measure the
texture of household tin/aluminum foil and make sure you see a fcc rolling
texture. You would have to analyze the data without any symmetry using
something like a 10th or 12th order spherical harmonics in the texture
analysis. If you can reproduce the rolling texture, your coverage is probably
sufficient for texture analysis and hence for a combined texture crystal
structure refinement of your actual sample. If not, you might have to do a
combined refinement against multiple patterns taken in different sample
orientations.
- An excellent book on the subject is Kocks/Wenk/Tome, "Texture and
Anisotropy", it has among a lot of other valuable information a few words on
the texture index and pretty much an atlas of possible textures for various
materials and processing conditions to help you judging whether the texture
you see makes sense.
- To my knowledge the only Rietveld software supporting the more powerful WIMV
and E-WIMV algorithms for texture (and also a somewhat improved "exponential
spherical harmonics" algorithm) is MAUD, freely available. Not sure what
flavors Topas supports, but it probably doesn't hurt to try different
programs. There are tutorials available on the MAUD website.
Hope this helps,
Sven
On Friday 18 April 2008 17:40:21 [EMAIL PROTECTED] wrote:
> Dear all,
>
> Now i am using the Topas Academic software to do the refinement of my
> sample which has stronger preferred orientations in some directions.
> In the program, i use the general spherical harmonics function to
> correlate the effect, as shown as below,
>
>
> 'Preferred Orientation using Spherical Harmonics
> PO_Spherical_Harmonics(sh, 6 load sh_Cij_prm {
> k00 !sh_c00 1.0000
> k41 sh_c41 0.36706`
> k61 sh_c61 -0.30246`
> } )
>
> And I see the literature, texture index J is used to evaluate the
> extent of PO by the equation shown in attachment ( I don't how to put
> the equation here).
>
> But I am not sure what the l means and itÂ’s not easy to find the
> detailed calculation in the literature. So I am wondering could
> someone of you give me some advice of the meaning of parameters m, n,
> l and in my case. Is the l is equal to 4 and 6?
>
> Thank you very much for all your help and time.
>
> Xiujun Li
> Master Student
> Advanced Materials and Processing Laboratory
> Chemical and Materials Engineering
> University of Alberta
> Edmonton, Alberta, Canada T6G 2G6
> Phone: 1-780-492-0701
