Editing Crystallography (section)

== Applications in various areas ==

=== Materials science ===
Crystallography is used by materials scientists to characterize different materials. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see macroscopically because the natural shapes of crystals reflect the atomic structure. In addition, physical properties are often controlled by crystalline defects. The understanding of crystal structures is an important prerequisite for understanding [[crystallographic defect]]s. Most materials do not occur as a single crystal, but are poly-crystalline in nature (they exist as an aggregate of small crystals with different orientations). As such, [[powder diffraction]] techniques, which take diffraction patterns of samples with a large number of crystals, play an important role in structural determination.

Other physical properties are also linked to crystallography. For example, the minerals in [[clay]] form small, flat, platelike structures. Clay can be easily deformed because the platelike particles can slip along each other in the plane of the plates, yet remain strongly connected in the direction perpendicular to the plates. Such mechanisms can be studied by crystallographic [[Texture (crystalline)|texture]] measurements. Crystallographic studies help elucidate the relationship between a material's structure and its properties, aiding in developing new materials with tailored characteristics. This understanding is crucial in various fields, including metallurgy, geology, and materials science. Advancements in crystallographic techniques, such as electron diffraction and X-ray crystallography, continue to expand our understanding of material behavior at the atomic level.

In another example, [[Iron#Allotropes|iron]] transforms from a [[body-centered cubic]] (bcc) structure called [[Allotropes of iron#Alpha iron (α-Fe)|ferrite]] to a [[face-centered cubic]] (fcc) structure called [[austenite]] when it is heated.<ref>{{Cite web |title=Materials Science and Engineering: An Introduction, 10th Edition {{!}} Wiley |url=https://www.wiley.com/en-us/Materials+Science+and+Engineering%3A+An+Introduction%2C+10th+Edition-p-9781119405498 |access-date=2022-09-10 |website=Wiley.com |language=en-us}}</ref> The fcc structure is a close-packed structure unlike the bcc structure; thus the volume of the iron decreases when this transformation occurs.

Crystallography is useful in phase identification. When manufacturing or using a material, it is generally desirable to know what compounds and what phases are present in the material, as their composition, structure and proportions will influence the material's properties. Each phase has a characteristic arrangement of atoms. X-ray or neutron diffraction can be used to identify which structures are present in the material, and thus which compounds are present. Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason is related to [[group theory#Chemistry and materials science|group theory]].
{{Further|Oligocrystalline material}}

=== Biology ===
[[X-ray crystallography]] is the primary method for determining the molecular conformations of biological [[macromolecule]]s, particularly [[protein]] and [[nucleic acid]]s such as [[DNA]] and [[RNA]]. The double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958, a three-dimensional model of the myoglobin molecule obtained by X-ray analysis.<ref>{{Cite journal | doi = 10.1038/181662a0| title = A Three-Dimensional Model of the Myoglobin Molecule Obtained by X-Ray Analysis| journal = Nature| volume = 181| issue = 4610| pages = 662–6| year = 1958| last1 = Kendrew | first1 = J. C.| last2 = Bodo | first2 = G.| last3 = Dintzis | first3 = H. M.| last4 = Parrish | first4 = R. G.| last5 = Wyckoff | first5 = H.| last6 = Phillips | first6 = D. C. | pmid=13517261|bibcode = 1958Natur.181..662K | s2cid = 4162786}}</ref> The [[Protein Data Bank]] (PDB) is a freely accessible repository for the structures of proteins and other biological macromolecules. Computer programs such as [[RasMol]], [[Pymol]] or [[Visual Molecular Dynamics|VMD]] can be used to visualize biological molecular structures.
[[Neutron crystallography]] is often used to help refine structures obtained by X-ray methods or to solve a specific bond; the methods are often viewed as complementary, as X-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly even off many light isotopes, including hydrogen and deuterium.
[[Electron diffraction]] has been used to determine some protein structures, most notably [[membrane protein]]s and [[viral capsid]]s.