See Help on X-Ray Diffraction.
Powder X-ray Diffraction (XRD) is one of the primary techniques used by mineralogists and solid state chemists to examine the physico-chemical make-up of unknown materials. This data is represented in a collection of single-phase X-ray powder diffraction patterns for the three most intense D values in the form of tables of interplanar spacings (D), relative intensities (I/Io), mineral name and chemical formulae
The XRD technique takes a sample of the material and places a powdered sample in a holder, then the sample is illuminated with x-rays of a fixed wave-length and the intensity of the reflected radiation is recorded using a goniometer. This data is then analyzed for the reflection angle to calculate the inter-atomic spacing (D value in Angstrom units - 10-8 cm). The intensity(I) is measured to discriminate (using I ratios) the various D spacings and the results are compared to this table to identify possible matches. Note: 2 theta (Θ) angle calculated from the Bragg Equation, 2 Θ = 2(arcsin(n λ/(2d)) where n=1
For more information about this technique, see X-Ray Analysis of a Solid or take an internet course at Birkbeck College On-line Courses. Many thanks to Frederic Biret for these data.
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Some important observations:
1. Minmax tolerance is % so that all D values with a +/- range in percent are returned. The default is 10%.
2. The wild card character for formula searches is "%" and is required, the search is case sensitive, and the order is important. For example, %K%Na% will give different results than %Na%K% depending on the order the element occurs in the formula.
3. You can use any combination of D1, D2, D3 and formula.
4. Try increasing the tolerance. The larger the tolerance, the more records are found.
5. Don't get too involved with complicated formula searches, one or two elements work best. Don't forget the % wild card in the search
6. You can reset the search by clicking here.