Difference between revisions of "Crystallography" - New World Encyclopedia
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| − | '''Crystallography''' | + | {{for|the book of poetry|Crystallography (book)}} |
| + | '''Crystallography''' is the experimental science of determining the arrangement of [[atom]]s in [[solid]]s. In older usage, it is the scientific study of [[crystal]]s. The word "crystallography" is derived from the [[Greek language|Greek]] words ''crystallon'' = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and ''graphein'' = write. | ||
| − | Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on the geometry of the crystals. This involves measuring the angles of crystal faces relative to theoretical reference axes ([[crystallographic axes]]), and establishing the [[symmetry]] of the crystal in question. The former is carried out using a [[goniometer]]. The position in 3D space of each crystal face is plotted on a stereographic net, e.g. [[ | + | Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on the geometry of the crystals. This involves measuring the angles of crystal faces relative to theoretical reference axes ([[crystallographic axes]]), and establishing the [[symmetry]] of the crystal in question. The former is carried out using a [[goniometer]]. The position in 3D space of each crystal face is plotted on a stereographic net, e.g. [[Wulff net]] or [[Lambert azimuthal equal-area projection|Lambert net]]. In fact, the [[pole (crystallography)|pole]] to each face is plotted on the net. Each point is labelled with its [[Miller index]]. The final plot allows the symmetry of the crystal to be established. |
| − | Crystallographic methods now | + | Crystallographic methods now depend on the analysis of the [[diffraction]] patterns that emerge from a sample that is targeted by a beam of some type. The beam is not always [[electromagnetic radiation]], even though [[X-ray]]s are the most common choice. For some purposes [[electron]]s or [[neutron]]s are used, which is possible due to the wave properties of the particles. Crystallographers often explicitly state the type of illumination used when referring to a method, as with the terms '''[[X-ray diffraction]],''' '''[[neutron diffraction]]''' and '''[[electron diffraction]].''' |
| − | + | These three types of radiation interact with the specimen in different ways. [[X-ray]]s interact with the spatial distribution of the [[valence electrons]], while [[electron]]s are [[charged particle]]s and therefore feel the total charge distribution of both the [[atomic nuclei]] and the surrounding electrons. [[Neutron]]s are scattered by the atomic nuclei through the [[strong nuclear force]]s, but in addition, the [[magnetic moment]] of neutrons is non-zero. They are therefore also scattered by [[magnetic field]]s. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies. | |
| − | |||
| − | + | == Theory == | |
| + | |||
| + | An image of a small object is usually generated by using a [[Lens (optics)|lens]] to focus the illuminating radiation, as is done with the rays of the [[optical spectrum|visible spectrum ]] in light [[microscope|microscopy]]. However, the wavelength of visible light (about 4000 to 7000 [[Angstrom]]s) is three [[order of magnitude|orders of magnitude]] longer then the length of typical [[chemical bond|atomic bonds]] and [[atom]]s themselves (about 1 to 2 Angstroms). | ||
| + | Therefore, obtaining information about the spatial arrangement of atoms requires the use of radiation with shorter wavelengths, such as X-rays. Employing shorter wavelengths implied abandoning microscopy and true imaging, however, because there exists no material from which a lens capable of focusing this type of radiation can be created. (That said, scientists have had some success focusing X-rays with microscopic [[Fresnel zone plate]]s made from gold, and by critical-angle reflection inside long tapered capillaries). Diffracted x-ray beams cannot be focussed to produce images, so the sample structure must be reconstructed from the diffraction pattern. Sharp features in the diffraction pattern arise from periodic, repeating structure in the sample, which are often very strong due to coherent reflection of many photons from many regularly spaced instances of similar structure, while non-periodic components of the structure result in diffuse (and usually weak) diffraction features. | ||
| + | |||
| + | Because of their highly ordered and repetitive structure, crystals give diffraction patterns of sharp [[Bragg reflection]] spots, and are ideal for analyzing the structure of solids. | ||
| + | |||
| + | == Notation ==<!-- This section is linked from [[Ion implantation]] —> | ||
| − | |||
See [[Miller index]] for a full treatment of this topic. | See [[Miller index]] for a full treatment of this topic. | ||
| − | * Coordinates in ''square [[bracket]]s'' such as '''<nowiki>[100]</nowiki>''' denote a direction (in real space). | + | * Coordinates in ''square [[bracket]]s'' such as '''<nowiki>[100]</nowiki>''' denote a direction vector (in real space). |
| − | * Coordinates in ''angle brackets'' or ''chevrons'' such as ''' | + | * Coordinates in ''angle brackets'' or ''chevrons'' such as '''<100>''' denote a ''family'' of directions which are related by symmetry operations. In the cubic crystal system for example, '''<100>''' would mean <nowiki>[100], [010], [001]</nowiki> or the negative of any of those directions. |
| − | * | + | * Miller indices in ''parentheses'' such as '''(100)''' denote a plane of the crystal structure, and regular repetitions of that plane with a particular spacing. In the cubic system, the [[surface normal|normal]] to the (hkl) plane is the direction [hkl], but in lower-symmetry cases, the normal to (hkl) is not parallel to [hkl]. |
| − | * | + | * Indices in ''curly brackets'' or ''braces'' such as '''<nowiki>{100}</nowiki>''' denote a family of planes and their normals which are equivalent due to symmetry operations, much the way angle brackets denote a family of directions. |
| − | ==Technique== | + | == Technique == |
| − | Some materials studied using crystallography, | + | Some materials studied using crystallography, [[protein]]s for example, do not occur naturally as crystals. Typically, such molecules are placed in solution and allowed to crystallize over days, weeks, or months through vapor [[diffusion]]. A drop of solution containing the molecule, buffer, and precipitants is sealed in a container with a reservoir containing a [[hygroscopic]] solution. Water in the drop diffuses to the reservoir, slowly increasing the concentration and allowing a crystal to form. If the concentration were to rise more quickly, the molecule would simply [[Precipitation (chemistry)|precipitate]] out of solution, resulting in disorderly granules rather than an orderly and hence usable crystal. |
| − | Once a crystal is obtained, data can be collected using a beam of radiation. Although many universities that engage in crystallographic research have their own X-ray producing equipment, [[Synchrotron light| | + | Once a crystal is obtained, data can be collected using a beam of radiation. Although many universities that engage in crystallographic research have their own X-ray producing equipment, [[Synchrotron light|synchrotron]]s are often used as X-ray sources, because of the purer and more complete patterns such sources can generate. Synchrotron sources also have a much higher intensity of X-ray beams, so data collection takes a fraction of the time normally necessary at weaker sources. |
Producing an image from a diffraction pattern requires sophisticated [[mathematics]] and often an iterative process of '''modelling and refinement.''' In this process, the mathematically predicted diffraction patterns of an hypothesized or "model" structure are compared to the actual pattern generated by the crystalline sample. Ideally, researchers make several initial guesses, which through refinement all converge on the same answer. Models are refined until their predicted patterns match to as great a degree as can be achieved without radical revision of the model. This is a painstaking process, made much easier today by computers. | Producing an image from a diffraction pattern requires sophisticated [[mathematics]] and often an iterative process of '''modelling and refinement.''' In this process, the mathematically predicted diffraction patterns of an hypothesized or "model" structure are compared to the actual pattern generated by the crystalline sample. Ideally, researchers make several initial guesses, which through refinement all converge on the same answer. Models are refined until their predicted patterns match to as great a degree as can be achieved without radical revision of the model. This is a painstaking process, made much easier today by computers. | ||
| − | The mathematical methods for the analysis of diffraction data only apply to ''patterns,'' which in turn result only when waves diffract from orderly arrays. Hence crystallography applies for the most part only to crystals, or to molecules which can be coaxed to | + | The mathematical methods for the analysis of diffraction data only apply to ''patterns,'' which in turn result only when waves diffract from orderly arrays. Hence crystallography applies for the most part only to crystals, or to molecules which can be coaxed to crystallize for the sake of measurement. In spite of this, a certain amount of molecular information can be deduced from the patterns that are generated by fibers and [[powder diffraction|powders]], which while not as perfect as a solid crystal, may exhibit a degree of order. This level of order can be sufficient to deduce the structure of simple molecules, or to determine the coarse features of more complicated molecules (the double-helical structure of [[DNA]], for example, was deduced from an X-ray diffraction pattern that had been generated by a fibrous sample). |
| − | == | + | ==Crystallography in materials engineering== |
| − | Crystallography is a tool that is often employed by materials scientists. 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. | + | Crystallography is a tool that is often employed by materials scientists. 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. Mostly, materials do not occur in a single crystalline, but poly-crystalline form, such that the [[powder diffraction]] method plays a most important role in structural determination. |
| − | A number of other physical properties are 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. | + | A number of other physical properties are 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. |
| − | In another example, [[iron]] transforms from a [[body-centered cubic]] (bcc) structure to a [[face-centered cubic]] (fcc) structure called austenite when it is heated. The fcc structure is a close-packed structure, and the bcc structure is not, which explains why the volume of the iron decreases when this transformation occurs. | + | In another example, [[iron]] transforms from a [[body-centered cubic]] (bcc) structure to a [[face-centered cubic]] (fcc) structure called [[austenite]] when it is heated. The fcc structure is a close-packed structure, and the bcc structure is not, which explains why the volume of the iron decreases when this transformation occurs. |
| − | Crystallography is useful in phase identification | + | Crystallography is useful in phase identification. When performing any process on a material, it may be desired to find out what compounds and what phases are present in the material. Each phase has a characteristic arrangement of atoms. Techniques like X-ray diffraction can be used to identify which patterns are present in the material, and thus which compounds are present (note: the determination of the "phases" within a material should not be confused with the more general problem of "phase determination," which refers to the phase of waves as they diffract from planes within a crystal, and which is a necessary step in the interpretation of complicated diffraction patterns). |
| − | Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason has a relation to group theory and geometry. See [[ | + | Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason has a relation to group theory and geometry. See [[symmetry group]]. |
| − | ==Biology== | + | == 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]]. In fact, the double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958 (Kendrew, J.C. et al. (1958) A three-dimensional model of the myoglobin molecule obtained by X-ray analysis | + | [[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]]. In fact, the double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958 (Kendrew, J.C. et al. (1958) A three-dimensional model of the myoglobin molecule obtained by X-ray analysis ([[Nature (journal)|''Nature'']] 181, 662–666). The [[Protein Data Bank]] (PDB) is a freely accessible repository for the structures of [[protein]]s and other biological macromolecules. Computer programs like [[RasMol]] or [[Pymol]] can be used to visualize biological molecular structures. |
[[Electron crystallography]] has been used to determine some protein structures, most notably [[membrane protein]]s and [[viral capsid]]s. | [[Electron crystallography]] has been used to determine some protein structures, most notably [[membrane protein]]s and [[viral capsid]]s. | ||
| + | |||
| + | ==Scientists of note== | ||
| + | <div style="-moz-column-count:3; column-count:3;"> | ||
| + | * [[William Henry Bragg]] | ||
| + | * [[William Lawrence Bragg]] | ||
| + | * [[Auguste Bravais]] | ||
| + | * [[Pierre Curie]] | ||
| + | * [[Francis Crick]] | ||
| + | * [[Boris Delone]] | ||
| + | * [[Paul Peter Ewald]] | ||
| + | * [[Rosalind Franklin]] | ||
| + | * [[Georges Friedel]] | ||
| + | * [[René Just Haüy]] | ||
| + | * [[Carl Hermann]] | ||
| + | * [[Dorothy Crowfoot Hodgkin]] | ||
| + | * [[Robert Huber]] | ||
| + | * [[Ernest-François Mallard]] | ||
| + | * [[Charles-Victor Mauguin]] | ||
| + | * [[William Hallowes Miller]] | ||
| + | * [[Max Perutz]] | ||
| + | * [[Hugo Rietveld]] | ||
| + | * [[Jean-Baptiste L. Romé de l'Isle]] | ||
| + | * [[Constance Tipper]] | ||
| + | * [[Don Craig Wiley]] | ||
| + | * [[Ada Yonath]] | ||
| + | </div> | ||
==See also== | ==See also== | ||
| − | + | <div style="-moz-column-count:3; column-count:3;"> | |
| − | * [[ | + | * [[Atomic packing factor]] |
| + | * [[Crystal]] | ||
| + | * [[Crystal engineering]] | ||
* [[Crystal optics]] | * [[Crystal optics]] | ||
| − | * [[ | + | * [[Crystal system]] |
| − | * [[ | + | * [[Crystallite]] |
| − | * [[diffraction]] | + | * [[Crystallization processes]] |
| − | * [[ | + | * [[Crystallographic database]] |
| − | * [[ | + | * [[Crystallographic group]] |
| + | * [[Diffraction]] | ||
| + | * [[Dynamical theory of diffraction]] | ||
| + | * [[Electron crystallography]] | ||
| + | * [[Powder diffraction]] | ||
| + | * [[Symmetry group]] | ||
* [[X-ray crystallography]] | * [[X-ray crystallography]] | ||
| − | + | </div> | |
| − | ==External links== | + | == External links == |
* [http://www.rockhounds.com/rockshop/xtal/index.html Introduction to Crystallography and Mineral Crystal Systems] | * [http://www.rockhounds.com/rockshop/xtal/index.html Introduction to Crystallography and Mineral Crystal Systems] | ||
| − | * [http://www. | + | * [http://www.mineralogie.uni-wuerzburg.de/links/teach/crysteach.html Crystallographic Teaching Pamphlets] |
* [http://cst-www.nrl.navy.mil/lattice/spcgrp/ Crystal Lattice Structures] | * [http://cst-www.nrl.navy.mil/lattice/spcgrp/ Crystal Lattice Structures] | ||
* [http://www.ccp14.ac.uk/ Freely Available Crystallographic Software for Academia] | * [http://www.ccp14.ac.uk/ Freely Available Crystallographic Software for Academia] | ||
| + | * [http://www.netsci.org/Resources/Software/Struct/xray.html NetSci Software Listing for Crystallography] | ||
| + | * [http://www.iucr.org/sincris-top/ SINCRIS Information Server for Crystallography] | ||
| + | * [http://www.chem.gla.ac.uk/~louis/software/ortep3/download.html ORTEP a professional grade viewer for use on a PC which is based on the FORTRAN code which came from Oak Ridge] | ||
| + | * [http://www.vega.org.uk Vega Science Trust Interviews on Crystallography] Freeview video interviews with Max Pertuz, Rober Huber and Aaron Klug. | ||
| + | *[http://www.iucr.org/iucr-top/comm/cteach/pamphlets.html Commission on Crystallographic Teaching, Pamphlets] | ||
| + | *[http://www.jcrystal.com/steffenweber/ Crystallography site of Steffen Weber with lots of Java Applets] | ||
| + | *[http://reference.iucr.org/dictionary/Main_Page IUCr Online Dictionary of Crystallography] | ||
| + | *[http://aca.hwi.buffalo.edu/ American Crystallographic Association] | ||
| + | *[http://www.geocities.com/psistar@sbcglobal.net/Laue.pdf Laue Measurement of Single-Crystal Turbine Blades] | ||
| + | *[http://www.mcbmm.ameslab.gov/index.html Ames Laboratory, US DOE Crystallography Research Resources] | ||
| − | [[Category: | + | [[Category:Crystallography| ]] |
| − | [[Category: | + | [[Category:Neutron related techniques]] |
| − | [[Category: | + | [[Category:Synchrotron related techniques]] |
| − | |||
| + | [[ar:علم البلورات]] | ||
| + | [[an:Cristalografía]] | ||
| + | [[bg:Кристалография]] | ||
| + | [[ca:Cristal·lografia]] | ||
| + | [[cs:Krystalografie]] | ||
[[da:Krystallografi]] | [[da:Krystallografi]] | ||
[[de:Kristallographie]] | [[de:Kristallographie]] | ||
[[et:Kristallograafia]] | [[et:Kristallograafia]] | ||
| + | [[el:Κρυσταλλογραφία]] | ||
[[es:Cristalografía]] | [[es:Cristalografía]] | ||
[[eo:Kristalografio]] | [[eo:Kristalografio]] | ||
| + | [[eu:Kristalografia]] | ||
| + | [[fa:بلورشناسی]] | ||
[[fr:Cristallographie]] | [[fr:Cristallographie]] | ||
| + | [[gl:Cristalografía]] | ||
| + | [[hr:Kristalografija]] | ||
| + | [[ia:Crystallographia]] | ||
| + | [[is:Kristallafræði]] | ||
| + | [[it:Cristallografia]] | ||
| + | [[he:קריסטלוגרפיה]] | ||
| + | [[lv:Kristalogrāfija]] | ||
| + | [[lb:Kristallographie]] | ||
| + | [[lt:Kristalografija]] | ||
[[nl:Kristallografie]] | [[nl:Kristallografie]] | ||
[[ja:結晶学]] | [[ja:結晶学]] | ||
| + | [[no:Krystallografi]] | ||
[[pl:Krystalografia]] | [[pl:Krystalografia]] | ||
| + | [[pt:Cristalografia]] | ||
| + | [[ro:Cristalografie]] | ||
[[ru:Кристаллография]] | [[ru:Кристаллография]] | ||
| + | [[sk:Kryštalografia]] | ||
[[tl:Crystallography]] | [[tl:Crystallography]] | ||
| − | [[tr: | + | [[ta:படிகவுருவியல்]] |
| − | [[zh: | + | [[th:ผลิกศาสตร์]] |
| − | + | [[tr:Kristalografi]] | |
| − | + | [[zh:晶体学]] | |
Revision as of 22:00, 27 September 2008
Crystallography is the experimental science of determining the arrangement of atoms in solids. In older usage, it is the scientific study of crystals. The word "crystallography" is derived from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write.
Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on the geometry of the crystals. This involves measuring the angles of crystal faces relative to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question. The former is carried out using a goniometer. The position in 3D space of each crystal face is plotted on a stereographic net, e.g. Wulff net or Lambert net. In fact, the pole to each face is plotted on the net. Each point is labelled with its Miller index. The final plot allows the symmetry of the crystal to be established.
Crystallographic methods now depend on the analysis of the diffraction patterns that emerge from a sample that is targeted by a beam of some type. The beam is not always electromagnetic radiation, even though X-rays are the most common choice. For some purposes electrons or neutrons are used, which is possible due to the wave properties of the particles. Crystallographers often explicitly state the type of illumination used when referring to a method, as with the terms X-ray diffraction, neutron diffraction and electron diffraction.
These three types of radiation interact with the specimen in different ways. X-rays interact with the spatial distribution of the valence electrons, while electrons are charged particles and therefore feel the total charge distribution of both the atomic nuclei and the surrounding electrons. Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero. They are therefore also scattered by magnetic fields. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies.
Theory
An image of a small object is usually generated by using a lens to focus the illuminating radiation, as is done with the rays of the visible spectrum in light microscopy. However, the wavelength of visible light (about 4000 to 7000 Angstroms) is three orders of magnitude longer then the length of typical atomic bonds and atoms themselves (about 1 to 2 Angstroms). Therefore, obtaining information about the spatial arrangement of atoms requires the use of radiation with shorter wavelengths, such as X-rays. Employing shorter wavelengths implied abandoning microscopy and true imaging, however, because there exists no material from which a lens capable of focusing this type of radiation can be created. (That said, scientists have had some success focusing X-rays with microscopic Fresnel zone plates made from gold, and by critical-angle reflection inside long tapered capillaries). Diffracted x-ray beams cannot be focussed to produce images, so the sample structure must be reconstructed from the diffraction pattern. Sharp features in the diffraction pattern arise from periodic, repeating structure in the sample, which are often very strong due to coherent reflection of many photons from many regularly spaced instances of similar structure, while non-periodic components of the structure result in diffuse (and usually weak) diffraction features.
Because of their highly ordered and repetitive structure, crystals give diffraction patterns of sharp Bragg reflection spots, and are ideal for analyzing the structure of solids.
Notation
See Miller index for a full treatment of this topic.
- Coordinates in square brackets such as [100] denote a direction vector (in real space).
- Coordinates in angle brackets or chevrons such as <100> denote a family of directions which are related by symmetry operations. In the cubic crystal system for example, <100> would mean [100], [010], [001] or the negative of any of those directions.
- Miller indices in parentheses such as (100) denote a plane of the crystal structure, and regular repetitions of that plane with a particular spacing. In the cubic system, the normal to the (hkl) plane is the direction [hkl], but in lower-symmetry cases, the normal to (hkl) is not parallel to [hkl].
- Indices in curly brackets or braces such as {100} denote a family of planes and their normals which are equivalent due to symmetry operations, much the way angle brackets denote a family of directions.
Technique
Some materials studied using crystallography, proteins for example, do not occur naturally as crystals. Typically, such molecules are placed in solution and allowed to crystallize over days, weeks, or months through vapor diffusion. A drop of solution containing the molecule, buffer, and precipitants is sealed in a container with a reservoir containing a hygroscopic solution. Water in the drop diffuses to the reservoir, slowly increasing the concentration and allowing a crystal to form. If the concentration were to rise more quickly, the molecule would simply precipitate out of solution, resulting in disorderly granules rather than an orderly and hence usable crystal.
Once a crystal is obtained, data can be collected using a beam of radiation. Although many universities that engage in crystallographic research have their own X-ray producing equipment, synchrotrons are often used as X-ray sources, because of the purer and more complete patterns such sources can generate. Synchrotron sources also have a much higher intensity of X-ray beams, so data collection takes a fraction of the time normally necessary at weaker sources.
Producing an image from a diffraction pattern requires sophisticated mathematics and often an iterative process of modelling and refinement. In this process, the mathematically predicted diffraction patterns of an hypothesized or "model" structure are compared to the actual pattern generated by the crystalline sample. Ideally, researchers make several initial guesses, which through refinement all converge on the same answer. Models are refined until their predicted patterns match to as great a degree as can be achieved without radical revision of the model. This is a painstaking process, made much easier today by computers.
The mathematical methods for the analysis of diffraction data only apply to patterns, which in turn result only when waves diffract from orderly arrays. Hence crystallography applies for the most part only to crystals, or to molecules which can be coaxed to crystallize for the sake of measurement. In spite of this, a certain amount of molecular information can be deduced from the patterns that are generated by fibers and powders, which while not as perfect as a solid crystal, may exhibit a degree of order. This level of order can be sufficient to deduce the structure of simple molecules, or to determine the coarse features of more complicated molecules (the double-helical structure of DNA, for example, was deduced from an X-ray diffraction pattern that had been generated by a fibrous sample).
Crystallography in materials engineering
Crystallography is a tool that is often employed by materials scientists. 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 defects. Mostly, materials do not occur in a single crystalline, but poly-crystalline form, such that the powder diffraction method plays a most important role in structural determination.
A number of other physical properties are 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 measurements.
In another example, iron transforms from a body-centered cubic (bcc) structure to a face-centered cubic (fcc) structure called austenite when it is heated. The fcc structure is a close-packed structure, and the bcc structure is not, which explains why the volume of the iron decreases when this transformation occurs.
Crystallography is useful in phase identification. When performing any process on a material, it may be desired to find out what compounds and what phases are present in the material. Each phase has a characteristic arrangement of atoms. Techniques like X-ray diffraction can be used to identify which patterns are present in the material, and thus which compounds are present (note: the determination of the "phases" within a material should not be confused with the more general problem of "phase determination," which refers to the phase of waves as they diffract from planes within a crystal, and which is a necessary step in the interpretation of complicated diffraction patterns).
Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason has a relation to group theory and geometry. See symmetry group.
Biology
X-ray crystallography is the primary method for determining the molecular conformations of biological macromolecules, particularly protein and nucleic acids such as DNA and RNA. In fact, the double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958 (Kendrew, J.C. et al. (1958) A three-dimensional model of the myoglobin molecule obtained by X-ray analysis (Nature 181, 662–666). The Protein Data Bank (PDB) is a freely accessible repository for the structures of proteins and other biological macromolecules. Computer programs like RasMol or Pymol can be used to visualize biological molecular structures.
Electron crystallography has been used to determine some protein structures, most notably membrane proteins and viral capsids.
Scientists of note
- William Henry Bragg
- William Lawrence Bragg
- Auguste Bravais
- Pierre Curie
- Francis Crick
- Boris Delone
- Paul Peter Ewald
- Rosalind Franklin
- Georges Friedel
- René Just Haüy
- Carl Hermann
- Dorothy Crowfoot Hodgkin
- Robert Huber
- Ernest-François Mallard
- Charles-Victor Mauguin
- William Hallowes Miller
- Max Perutz
- Hugo Rietveld
- Jean-Baptiste L. Romé de l'Isle
- Constance Tipper
- Don Craig Wiley
- Ada Yonath
See also
- Atomic packing factor
- Crystal
- Crystal engineering
- Crystal optics
- Crystal system
- Crystallite
- Crystallization processes
- Crystallographic database
- Crystallographic group
- Diffraction
- Dynamical theory of diffraction
- Electron crystallography
- Powder diffraction
- Symmetry group
- X-ray crystallography
External links
- Introduction to Crystallography and Mineral Crystal Systems
- Crystallographic Teaching Pamphlets
- Crystal Lattice Structures
- Freely Available Crystallographic Software for Academia
- NetSci Software Listing for Crystallography
- SINCRIS Information Server for Crystallography
- ORTEP a professional grade viewer for use on a PC which is based on the FORTRAN code which came from Oak Ridge
- Vega Science Trust Interviews on Crystallography Freeview video interviews with Max Pertuz, Rober Huber and Aaron Klug.
- Commission on Crystallographic Teaching, Pamphlets
- Crystallography site of Steffen Weber with lots of Java Applets
- IUCr Online Dictionary of Crystallography
- American Crystallographic Association
- Laue Measurement of Single-Crystal Turbine Blades
- Ames Laboratory, US DOE Crystallography Research Resources
ar:علم البلورات an:Cristalografía bg:Кристалография ca:Cristal·lografia cs:Krystalografie da:Krystallografi de:Kristallographie et:Kristallograafia el:Κρυσταλλογραφία es:Cristalografía eo:Kristalografio eu:Kristalografia fa:بلورشناسی fr:Cristallographie gl:Cristalografía hr:Kristalografija ia:Crystallographia is:Kristallafræði it:Cristallografia he:קריסטלוגרפיה lv:Kristalogrāfija lb:Kristallographie lt:Kristalografija nl:Kristallografie ja:結晶学 no:Krystallografi pl:Krystalografia pt:Cristalografia ro:Cristalografie ru:Кристаллография sk:Kryštalografia tl:Crystallography ta:படிகவுருவியல் th:ผลิกศาสตร์ tr:Kristalografi zh:晶体学
