Solid samples with polished surfaces, thin films and liquids can be measured directly by XRD. The pre-treatments for powder samples are critical to minimize source errors:
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Obtain a few tenths of a gram (or more) of the material, as pure as possible
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Grind the sample to a fine powder, typically in a fluid to minimize inducing extra strain that can offset peak positions, and to randomize orientation. Powder less than ~10 μm(or 200-mesh) in size is preferred
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Place into a sample holder or onto the sample surface choosing one of the following methods:
a) smear uniformly onto a glass slide, assuring a flat upper surface
b) pack into a sample container
c) sprinkle on double sticky tape
(Typically the substrate is amorphous to avoid interference)
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Care must be taken to create a flat upper surface and to achieve a random distribution of lattice orientations unless creating an oriented smear
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For analysis of clays which require a single orientation, specialized techniques for preparation of clay samples are given by US Geological Survey (USGS)
- For unit cell determinations, a small amount of a standard with known peak positions (that do not interfere with the sample) can be added and used to correct peak positions.