For accurate determination you first need to make a database with alloys of known composition mapping their corresponding lattice parameters. The standard powder diffraction databases are normally not very useful for this purpose (few sample constitutions, varying thermomechanical preprocessing conditions, etc)
After having the data base established, you may determine the constitution of unknown samples fitting the lattice parameters extracted from Rietveld refinement against your PXRD data, to an interpolated function between your data base points.
The following critical issues should be noted:
1) The "vegards law"-type relationship linking solid solution in the parent lattice with a corresponding (mean field) elongation of the lattice parameter, may not be linear nor fully differentiable over extended regions, even for binary systems. For ternary or higher-order systems, concentration-lattice parameter relationships can become very complex.
2) Since you are measuring the elongation of the lattice due to solid solution, the accuracy of the method is highly questionable when samples have been subjected to different forms or levels of mechanical processing, i.e.yielding different concentrations of defects (dislocations, vacancies, etc.)
3) Use the full PXRD pattern with peaks at high scattering angles and Rietveld refinement to extract your lattice parameter. Use proper error propagation methods to assess accuracies.
Thnks... but if I am mixing a set of known compositions of metal salts doesn't mean that it will form alloy in that ratio.... can u suggest some references how to standardise these parameters ?
Like I said in my first answer. If you want to determine the level of alloying by reasonable precision in solid solution by matching lattice parameters determined by XRD, you need to build a database of alloys with known compositions. Otherwise, I would suggest use of a spectroscopic method.
Thanks ragnvald for ur replies... Can u suggest some references that might be useful in this aspect, mainly how these standardisations are preformed ... I am new to this alloy composition determination filed...so...
A useful starting point would be a comprehensive textbook on XRD, e.g. Fundamentals of Crystallography by Giaccovazzo et al, IUCr Oxford Press, perhaps supplemented by "The Rietveld Method" by R. A. Young
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