Talk:Powder diffraction

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"Neutrons are only available at a small number of nuclear reactors in the world."

I'm sorry, but when did neutrons stop being at the heart of nearly all atoms and become some rare thing that only exists in reactors?

Need someone that understands the subject to clarify if this is speaking about high energy neutrons as radiation or what.

Neutrons are indeed in every atom (well, barring Hydrogen), but you need free neutrons not at the core of an atom for diffraction, with a wavelength close to 1Å so that it can be diffracted by the crystal lattice. Only suitable for this are research reactors and spallation sources (and only a few of thoses are actually used for materials reserch). I have added links to reflect that. VincentFavreNicolin 22:17, 8 January 2006 (UTC)

Powder x-ray diffraction does not use neutrons, but rather electrons, generally powered by a potential of 30,000V

Well, actually it uses x-rays, though they're produced using electrons.AlmostReadytoFly 20:30, 30 August 2006 (UTC)

Some confusion above. X-ray diffraction can be done in a laboratory with the K-alpha-1 characteristic peak, the consequence of electrons being rapidly decelerated. Alternativley, one can use accelerated electrons which due to wave-particle duality exhibit a wavelength of X-rays. Whether one uses X-rays or neutrons depends on what you want to measure.

1 Orientation Effect
2 Invention
3 Peak Broadening
4 Rewrite 2007-02

[edit] Orientation Effect

Could use a paragraph or two on preferred orientation effect

[edit] Invention

I'm told (by people at the Paul Scherrer Institute) that the powder diffraction method is also called the Debye-Scherrer method, after its inventors. Perhaps this merits mention?AlmostReadytoFly 20:23, 30 August 2006 (UTC)

[edit] Peak Broadening

The Scherer method is one of the more primitive ways of analysing the broadening of X-ray peaks, but can be useful in some regards.
Peaks are generally regarded to be broadened by three different effects; instrumental, size and strain. Although, for the most part size and strain are said to be separate entities there is a certain amount of overlap. For example, dislocations would be included in both as they are part of grain boundaries and cause lattice strain.
To get rid of the instrumental effect two methods are utilised either Stokes Fourier deconvolution method or the Reitveld method. The next step is to separate the size effect from the strain effect.
The size and strain profiles can both be described by Voight functions and the size part is independent of the angle or plane. This, and finding the integral breadth of the peaks, forms the basis of the double Voight method. Alternatively, one may undertake a Fourier analysis and use the Warren-Averbach formula to separate the two.
Whilst the peak shift is often thought to be mainly due to long-range internal stresses, the lattice strain can be found with the sin squared phi method, the broadening of the peaks is in normally attributed to dislocations due to its strain field that decreases as 1/r, less than other defects. However, other factors should not be ignored, as stacking faults can in some materials cause more broadening and recent evidence suggests (Levine et al 06) that strain varies considerably between dislocations cells.

IUCR Monographs, Defect and microstructure analysis by diffraction, Chapter 7,
LYLE E. LEVINE1* et al ; X-ray microbeam measurements of individual dislocation cell elastic strains in deformed single-crystal copper; nature materials; VOL 5; 619; AUGUST 2006
R. Kužel;Dislocation line broadening; Z. Kristallogr. Suppl. 23 (2006) 75-80 75
--[00:15, 16 November 2006 (UTC)Hadfield Simm

[edit] Rewrite 2007-02

In case it is not clear, I am approaching this from a materials science / physics point of view, and any balance is welcome. Particularly, if someone wants to offer a better explanation under the crystallinity subsection, and how to deconvolute the amorphous background from the inelastic scattering background which exists even for perfect crystals.

I reorganized a bit and pared several full sentences which appeared redundant - please edit or leave a note here if anything significant has been omitted from this version.

Moved momentum transfer out of the intro for clarity - Bragg scattering is an elastic process, inelastic x-ray scattering is completely different. Change in incident wave vector = reciprocal lattice vector is covered under both reciprocal lattice and Bragg scattering. I suspect that most people who are unfamiliar with the topic would expect a change in the magnitude of the momentum, not just direction.

There was an html list immediately following the Uses section; it did not correspond to the succeeding sections, and Wikipedia generates a table of contents automagically, so I removed it. Some of these items should be given their own subsections, though, so I have reproduced it here: