XRD is often used to identify and characterise known as
well as unknown organic and inorganic crystalline materials. Each material
forms a unique diffraction peak which is also called the ‘fingerprint’ of the
material. Usually the strongest three beam or peaklines are used to
characterize each material.These beams are compared to the data available with
the ICDD (International Centre for Diffraction Data) formerly JCPDS (Joint
Committee for Powder Diffraction Standards). The indexed data includes cell
parameters, the density as well as the chemistry of the material so
identification becomes easier. X-ray
diffraction patterns are so accurate that they can even point out if the
materials are pure or if they contain any impurities.
Modern XRD instrumentation in testing laboratories is
usually pre-loaded with the standard pattern or they have a licence which gives
them access to the ICDD data. It becomes easy with the automatic search and
indexing to identify the material as the automatic search provides a possible
combination of elements which can be used to index the pattern. The original reason for undertaking to do XRD was
to identify the structure of the unknown material. Of course when the material
is composed of single crystals the identification process
is easier but even for polycrystalline materials powder diffraction is used as
it provides information on the shape and size of a unit cell and the way atoms
are arranged in the cell. Also each of the chemical compounds or phase of the
mixture of compounds has a different diffraction pattern so the pattern. The
peaks are often classified as major, minor or trace which helps to identify the
phases more accurately.
XRD can be used on a number of materials to identify them
like materials that are crystal, amorphous or liquid and also monatomic gas.
Fortunately the pattern produced through X-ray diffraction
is not dependent on whether the material is a pure substance or is in a state
of physical mixture. It is still possible to identify the crystal structure of
the material as well as the percentage of the given material in a physical
mixture. This means that qualitative as well as quantitative analysis of the
material is possible. In other words through XRD it is possible to get
information on the state of the material.
X-ray diffraction has become a choice for testing all
kinds of materials correctly as the technique is powerful and accurate. Through
XRD patterns it is possible to analyse phases and the lattice parameter which
help to identify the unknown material. The change in diffraction pattern of
each compound is sometimes so slight that only an experienced XRD technician
can make out the difference. It is also
possible to study the texture and the strain of the material as XRD beam
pattern can show if the material has no strain, uniform strain or un-uniform
strain. It is possible to identify the texture of the material from the way the
grains are distributed in the sample material.