Diffraction types Flashcards
What do diffractometers measure?
2 theta and intensity
What does powder x-ray diffraction measure?
Electron clouds
How does PXRD work?
Xrays are fired at a crystal and are diffracted off areas of high electron density
What are some of the applications of PXRD?
Identification of unknown materials, determination of sample purity, determination of lattice parameters and crystal size
What are some of the limitations of PXRD?
There is an overlap of peaks when orientation of crystals are not random, larger atoms will dominate and so lighter atoms are difficult to detect, can’t distinguish between similarly sized atoms
How can you prevent an overlap of peaks?
Grind into even finer powder
What are the advantages of using single crystal diffraction?
Easier to solve and gives more accurate refinement
What are the disadvantages of using single crystal diffraction?
It is hard to grow single crystals for most inorganic solids
How does neutron diffraction work?
Beam of neutrons fired at sample and diffracted by atomic nuclei
What are some of the advantages of using neutron diffraction?
It can discriminate between similarly sized atoms, lighter atoms will show with equal intensity as larger ones and can show non-stoichiometry and feromagnetic qualities
Why can neutron diffraction show feromagnetic quantities?
Neutrons can have a half spin and so can be scattered by unpaired electrons
What are the disadvantages to using neutron diffraction?
Requires specialist equipment at specialist sites
What are the advantages to using x-ray or neutron diffraction over electron diffraction?
Much more sensitive (detecting trace amounts) and can focus of specific areas of a sample
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