In mathematics, physics and chemistry, a space group is the symmetry group of a configuration in space, usually in three dimensions.^{[1]} In three dimensions, there are 219 distinct types, or 230 if chiral copies are considered distinct. Space groups are also studied in dimensions other than 3 where they are sometimes called Bieberbach groups, and are discrete cocompact groups of isometries of an oriented Euclidean space.
In crystallography, space groups are also called the crystallographic or Fedorov groups, and represent a description of the symmetry of the crystal. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography (Hahn (2002)).
Space groups in 2 dimensions are the 17 wallpaper groups which have been known for several centuries, though the proof that the list was complete was only given in 1891, after the much more difficult classification of space groups had been completed.
In 1879 Leonhard Sohncke listed the 65 space groups (called Sohncke groups) whose elements preserve the orientation. More accurately, he listed 66 groups, but Fedorov and Schönflies both noticed that two of them were really the same. The space groups in three dimensions were first enumerated by Fedorov (1891) (whose list had two omissions (I43d and Fdd2) and one duplication (Fmm2)), and shortly afterwards were independently enumerated by Schönflies (1891) (whose list had four omissions (I43d, Pc, Cc, ?) and one duplication (P42_{1}m)). The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies. Barlow (1894) later enumerated the groups with a different method, but omitted four groups (Fdd2, I42d, P42_{1}d, and P42_{1}c) even though he already had the correct list of 230 groups from Fedorov and Schönflies; the common claim that Barlow was unaware of their work is a myth. Burckhardt (1967) describes the history of the discovery of the space groups in detail.
The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, each of the latter belonging to one of 7 lattice systems. This results in a space group being some combination of the translational symmetry of a unit cell including lattice centering, the point group symmetry operations of reflection, rotation and improper rotation (also called rotoinversion), and the screw axis and glide plane symmetry operations. The combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries.
The elements of the space group fixing a point of space are the identity element, reflections, rotations and improper rotations.
The translations form a normal abelian subgroup of rank 3, called the Bravais lattice. There are 14 possible types of Bravais lattice. The quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups. Translation is defined as the face moves from one point to another point.
A glide plane is a reflection in a plane, followed by a translation parallel with that plane. This is noted by a, b or c, depending on which axis the glide is along. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, which is a fourth of the way along either a face or space diagonal of the unit cell. The latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two perpendicular directions simultaneously, i.e. the same glide plane can be called b or c, a or b, a or c. For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb. In 1992, it was suggested to use symbol e for such planes. The symbols for five space groups have been modified:
Space group No. | 39 | 41 | 64 | 67 | 68 |
---|---|---|---|---|---|
New symbol | Aem2 | Aea2 | Cmce | Cmme | Ccce |
Old Symbol | Abm2 | Aba2 | Cmca | Cmma | Ccca |
A screw axis is a rotation about an axis, followed by a translation along the direction of the axis. These are noted by a number, n, to describe the degree of rotation, where the number is how many operations must be applied to complete a full rotation (e.g., 3 would mean a rotation one third of the way around the axis each time). The degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So, 2_{1} is a twofold rotation followed by a translation of 1/2 of the lattice vector.
The general formula for the action of an element of a space group is
y = M.x + D
where M is its matrix, D is its vector, and where the element transforms point x into point y. In general, D = D(lattice) + D(M), where D(M) is a unique function of M that is zero for M being the identity. The matrices M form a point group that is a basis of the space group; the lattice must be symmetric under that point group.
The lattice dimension can be less than the overall dimension, resulting in a "subperiodic" space group. For (overall dimension, lattice dimension):
There are at least ten methods of naming space groups. Some of these methods can assign several different names to the same space group, so altogether there are many thousands of different names.
There are (at least) 10 different ways to classify space groups into classes. The relations between some of these are described in the following table. Each classification system is a refinement of the ones below it.
(Crystallographic) space group types (230 in three dimensions). Two space groups, considered as subgroups of the group of affine transformations of space, have the same space group type if they are conjugate by an orientation-preserving affine transformation. In three dimensions, for 11 of the affine space groups, there is no orientation-preserving map from the group to its mirror image, so if one distinguishes groups from their mirror images these each split into two cases. So there are 54 + 11 = 65 space group types that preserve orientation. | |
Affine space group types (219 in three dimensions). Two space groups, considered as subgroups of the group of affine transformations of space, have the same affine space group type if they are conjugate under an affine transformation. The affine space group type is determined by the underlying abstract group of the space group. In three dimensions there are 54 affine space group types that preserve orientation. | |
Arithmetic crystal classes (73 in three dimensions). Sometimes called Z-classes. These are determined by the point group together with the action of the point group on the subgroup of translations. In other words, the arithmetic crystal classes correspond to conjugacy classes of finite subgroup of the general linear group GL_{n}(Z) over the integers. A space group is called symmorphic (or split) if there is a point such that all symmetries are the product of a symmetry fixing this point and a translation. Equivalently, a space group is symmorphic if it is a semidirect product of its point group with its translation subgroup. There are 73 symmorphic space groups, with exactly one in each arithmetic crystal class. There are also 157 nonsymmorphic space group types with varying numbers in the arithmetic crystal classes.
Arithmetic crystal classes may be interpreted as different orientations of the point groups in the lattice, with the group elements' matrix components being constrained to have integer coefficients in lattice space. This is rather easy to picture in the two-dimensional, wallpaper group case. Some of the point groups have reflections, and the reflection lines can be along the lattice directions, halfway in between them, or both.
| |
(geometric) Crystal classes (32 in three dimensions). Sometimes called Q-classes. The crystal class of a space group is determined by its point group: the quotient by the subgroup of translations, acting on the lattice. Two space groups are in the same crystal class if and only if their point groups, which are subgroups of GL_{n}(Z), are conjugate in the larger group GL_{n}(Q). | Bravais flocks (14 in three dimensions). These are determined by the underlying Bravais lattice type.
These correspond to conjugacy classes of lattice point groups in GL_{n}(Z), where the lattice point group is the group of symmetries of the underlying lattice that fix a point of the lattice, and contains the point group. |
Crystal systems. (7 in three dimensions) Crystal systems are an ad hoc modification of the lattice systems to make them compatible with the classification according to point groups. They differ from crystal families in that the hexagonal crystal family is split into two subsets, called the trigonal and hexagonal crystal systems. The trigonal crystal system is larger than the rhombohedral lattice system, the hexagonal crystal system is smaller than the hexagonal lattice system, and the remaining crystal systems and lattice systems are the same. | Lattice systems (7 in three dimensions). The lattice system of a space group is determined by the conjugacy class of the lattice point group (a subgroup of GL_{n}(Z)) in the larger group GL_{n}(Q). In three dimensions the lattice point group can have one of the 7 different orders 2, 4, 8, 12, 16, 24, or 48. The hexagonal crystal family is split into two subsets, called the rhombohedral and hexagonal lattice systems. |
Crystal families (6 in three dimensions). The point group of a space group does not quite determine its lattice system, because occasionally two space groups with the same point group may be in different lattice systems. Crystal families are formed from lattice systems by merging the two lattice systems whenever this happens, so that the crystal family of a space group is determined by either its lattice system or its point group. In 3 dimensions the only two lattice families that get merged in this way are the hexagonal and rhombohedral lattice systems, which are combined into the hexagonal crystal family. The 6 crystal families in 3 dimensions are called triclinic, monoclinic, orthorhombic, tetragonal, hexagonal, and cubic. Crystal families are commonly used in popular books on crystals, where they are sometimes called crystal systems. |
Conway, Delgado Friedrichs, and Huson et al. (2001) gave another classification of the space groups, called a fibrifold notation, according to the fibrifold structures on the corresponding orbifold. They divided the 219 affine space groups into reducible and irreducible groups. The reducible groups fall into 17 classes corresponding to the 17 wallpaper groups, and the remaining 35 irreducible groups are the same as the cubic groups and are classified separately.
In n dimensions, an affine space group, or Bieberbach group, is a discrete subgroup of isometries of n-dimensional Euclidean space with a compact fundamental domain. Bieberbach (1911, 1912) proved that the subgroup of translations of any such group contains n linearly independent translations, and is a free abelian subgroup of finite index, and is also the unique maximal normal abelian subgroup. He also showed that in any dimension n there are only a finite number of possibilities for the isomorphism class of the underlying group of a space group, and moreover the action of the group on Euclidean space is unique up to conjugation by affine transformations. This answers part of Hilbert's eighteenth problem. Zassenhaus (1948) showed that conversely any group that is the extension of Z^{n} by a finite group acting faithfully is an affine space group. Combining these results shows that classifying space groups in n dimensions up to conjugation by affine transformations is essentially the same as classifying isomorphism classes for groups that are extensions of Z^{n} by a finite group acting faithfully.
It is essential in Bieberbach's theorems to assume that the group acts as isometries; the theorems do not generalize to discrete cocompact groups of affine transformations of Euclidean space. A counter-example is given by the 3-dimensional Heisenberg group of the integers acting by translations on the Heisenberg group of the reals, identified with 3-dimensional Euclidean space. This is a discrete cocompact group of affine transformations of space, but does not contain a subgroup Z^{3}.
This table gives the number of space group types in small dimensions, including the numbers of various classes of space group. The numbers of enantiomorphic pairs are given in parentheses.
Dimensions | Crystal families (sequence A004032 in the OEIS) | Crystal systems (sequence A004031 in the OEIS) | Bravais lattices (sequence A004030 in the OEIS) | Abstract crystallographic point groups (sequence A006226 in the OEIS) | Geometric crystal classes, Q-classes, crystallographic point groups (sequence A004028 in the OEIS) | Arithmetic crystal classes, Z-classes (sequence A004027 in the OEIS) | Affine space group types (sequence A004029 in the OEIS) | Crystallographic space group types (sequence A006227 in the OEIS) |
---|---|---|---|---|---|---|---|---|
0^{a} | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
1^{b} | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 |
2^{c} | 4 | 4 | 5 | 9 | 10 | 13 | 17 | 17 |
3^{d} | 6 | 7 | 14 | 18 | 32 | 73 | 219 (+11) | 230 |
4^{e} | 23 (+6) | 33 (+7) | 64 (+10) | 118 | 227 (+44) | 710 (+70) | 4783 (+111) | 4894 |
5^{f} | 32 | 59 | 189 | 239 | 955 | 6079 | 222018 (+79) | 222097 |
6^{g} | 91 | 251 | 841 | 1594 | 7103 | 85308 (+?) | 28927915 (+?) | ? |
a - Trivial group
b - One is the group of integers and the other is the infinite dihedral group; see symmetry groups in one dimension
c - these 2D space groups are also called wallpaper groups or plane groups.
d - In 3D there are 230 crystallographic space group types, which reduces to 219 affine space group types because of some types being different from their mirror image; these are said to differ by "enantiomorphous character" (e.g. P3_{1}12 and P3_{2}12). Usually "space group" refers to 3D. They were enumerated independently by Barlow (1894), Fedorov (1891) and Schönflies (1891).
e - The 4895 4-dimensional groups were enumerated by Harold Brown, Rolf Bülow, and Joachim Neubüser et al. (1978). Neubüser, Souvignier & Wondratschek (2002) corrected the number of enantiomorphic groups from 112 to 111, so total number of groups is 4783+111=4894. There are 44 enantiomorphic point groups in 4-dimensional space. If we consider enantiomorphic groups as different, the total number of point groups is 227+44=271.
f - Plesken & Schulz (2000) enumerated the ones of dimension 5. Souvignier (2003) counted the enantiomorphs.
g - Plesken & Schulz (2000) enumerated the ones of dimension 6, later the corrected figures were found.^{[4]} Initially published number of 826 Lattice types in Plesken & Hanrath (1984) was corrected to 841 in Opgenorth, Plesken & Schulz (1998). See also Janssen et al. (2002). Souvignier (2003) counted the enantiomorphs, but that paper relied on old erroneous CARAT data for dimension 6.
In addition to crystallographic space groups there are also magnetic space groups (also called two-color (black and white) crystallographic groups or Shubnikov groups). These symmetries contain an element known as time reversal. They treat time as an additional dimension, and the group elements can include time reversal as reflection in it. They are of importance in magnetic structures that contain ordered unpaired spins, i.e. ferro-, ferri- or antiferromagnetic structures as studied by neutron diffraction. The time reversal element flips a magnetic spin while leaving all other structure the same and it can be combined with a number of other symmetry elements. Including time reversal there are 1651 magnetic space groups in 3D (Kim 1999, p.428). It has also been possible to construct magnetic versions for other overall and lattice dimensions (Daniel Litvin's papers, (Litvin 2008), (Litvin 2005)). Frieze groups are magnetic 1D line groups and layer groups are magnetic wallpaper groups, and the axial 3D point groups are magnetic 2D point groups. Number of original and magnetic groups by (overall, lattice) dimension:
Table of the wallpaper groups using the classification of the 3-dimensional space groups:
Crystal system (Bravais lattice) |
Geometric class Point group |
Arithmetic class |
Wallpaper groups (cell diagram) | ||||||
---|---|---|---|---|---|---|---|---|---|
Schön. | Orbifold notation | Cox. | Ord. | ||||||
Oblique |
C_{1} | (1) | [ ]^{+} | 1 | None | p1 (1) |
|||
C_{2} | (22) | [2]^{+} | 2 | None | p2 (2222) |
||||
Rectangular (Centered rhombic) |
D_{1} | (*) | [ ] | 2 | Along | pm (**) |
pg (××) |
||
D_{2} | (*22) | [2] | 4 | Along | pmm (*2222) |
pmg (22*) |
|||
Rhombic (Centered rectangular) |
D_{1} | (*) | [ ] | 2 | Between | cm (*×) |
|||
D_{2} | (*22) | [2] | 4 | Between | cmm (2*22) |
pgg (22×) |
|||
Square |
C_{4} | (44) | [4]^{+} | 4 | None | p4 (442) |
|||
D_{4} | (*44) | [4] | 8 | Both | p4m (*442) |
p4g (4*2) |
|||
Hexagonal |
C_{3} | (33) | [3]^{+} | 3 | None | p3 (333) |
|||
D_{3} | (*33) | [3] | 6 | Between | p3m1 (*333) |
p31m (3*3) |
|||
C_{6} | (66) | [6]^{+} | 6 | None | p6 (632) |
||||
D_{6} | (*66) | [6] | 12 | Both | p6m (*632) |
For each geometric class, the possible arithmetic classes are
# | Crystal system (count) Bravais lattice |
Point group | Space groups (international short symbol) | ||||
---|---|---|---|---|---|---|---|
Intl | Schön. | Orbifold notation | Cox. | Ord. | |||
1 | Triclinic (2) |
1 | C_{1} | 11 | [ ]^{+} | 1 | P1 |
2 | 1 | C_{i} | 1× | [2^{+},2^{+}] | 2 | P1 | |
3–5 | Monoclinic (13) |
2 | C_{2} | 22 | [2]^{+} | 2 | P2, P2_{1} C2 |
6–9 | m | C_{s} | *11 | [ ] | 2 | Pm, Pc Cm, Cc | |
10–15 | 2/m | C_{2h} | 2* | [2,2^{+}] | 4 | P2/m, P2_{1}/m C2/m, P2/c, P2_{1}/c C2/c | |
16–24 | Orthorhombic (59) |
222 | D_{2} | 222 | [2,2]^{+} | 4 | P222, P222_{1}, P2_{1}2_{1}2, P2_{1}2_{1}2_{1}, C222_{1}, C222, F222, I222, I2_{1}2_{1}2_{1} |
25–46 | mm2 | C_{2v} | *22 | [2] | 4 | Pmm2, Pmc2_{1}, Pcc2, Pma2, Pca2_{1}, Pnc2, Pmn2_{1}, Pba2, Pna2_{1}, Pnn2 Cmm2, Cmc2_{1}, Ccc2, Amm2, Aem2, Ama2, Aea2 Fmm2, Fdd2 Imm2, Iba2, Ima2 | |
47–74 | mmm | D_{2h} | *222 | [2,2] | 8 | Pmmm, Pnnn, Pccm, Pban, Pmma, Pnna, Pmna, Pcca, Pbam, Pccn, Pbcm, Pnnm, Pmmn, Pbcn, Pbca, Pnma Cmcm, Cmce, Cmmm, Cccm, Cmme, Ccce Fmmm, Fddd Immm, Ibam, Ibca, Imma | |
75–80 | Tetragonal (68) |
4 | C_{4} | 44 | [4]^{+} | 4 | P4, P4_{1}, P4_{2}, P4_{3}, I4, I4_{1} |
81–82 | 4 | S_{4} | 2× | [2^{+},4^{+}] | 4 | P4, I4 | |
83–88 | 4/m | C_{4h} | 4* | [2,4^{+}] | 8 | P4/m, P4_{2}/m, P4/n, P4_{2}/n I4/m, I4_{1}/a | |
89–98 | 422 | D_{4} | 224 | [2,4]^{+} | 8 | P422, P42_{1}2, P4_{1}22, P4_{1}2_{1}2, P4_{2}22, P4_{2}2_{1}2, P4_{3}22, P4_{3}2_{1}2 I422, I4_{1}22 | |
99–110 | 4mm | C_{4v} | *44 | [4] | 8 | P4mm, P4bm, P4_{2}cm, P4_{2}nm, P4cc, P4nc, P4_{2}mc, P4_{2}bc I4mm, I4cm, I4_{1}md, I4_{1}cd | |
111–122 | 42m | D_{2d} | 2*2 | [2^{+},4] | 8 | P42m, P42c, P42_{1}m, P42_{1}c, P4m2, P4c2, P4b2, P4n2 I4m2, I4c2, I42m, I42d | |
123–142 | 4/mmm | D_{4h} | *224 | [2,4] | 16 | P4/mmm, P4/mcc, P4/nbm, P4/nnc, P4/mbm, P4/mnc, P4/nmm, P4/ncc, P4_{2}/mmc, P4_{2}/mcm, P4_{2}/nbc, P4_{2}/nnm, P4_{2}/mbc, P4_{2}/mnm, P4_{2}/nmc, P4_{2}/ncm I4/mmm, I4/mcm, I4_{1}/amd, I4_{1}/acd | |
143–146 | Trigonal (25) |
3 | C_{3} | 33 | [3]^{+} | 3 | P3, P3_{1}, P3_{2} R3 |
147–148 | 3 | S_{6} | 3× | [2^{+},6^{+}] | 6 | P3, R3 | |
149–155 | 32 | D_{3} | 223 | [2,3]^{+} | 6 | P312, P321, P3_{1}12, P3_{1}21, P3_{2}12, P3_{2}21 R32 | |
156–161 | 3m | C_{3v} | *33 | [3] | 6 | P3m1, P31m, P3c1, P31c R3m, R3c | |
162–167 | 3m | D_{3d} | 2*3 | [2^{+},6] | 12 | P31m, P31c, P3m1, P3c1 R3m, R3c | |
168–173 | Hexagonal (27) |
6 | C_{6} | 66 | [6]^{+} | 6 | P6, P6_{1}, P6_{5}, P6_{2}, P6_{4}, P6_{3} |
174 | 6 | C_{3h} | 3* | [2,3^{+}] | 6 | P6 | |
175–176 | 6/m | C_{6h} | 6* | [2,6^{+}] | 12 | P6/m, P6_{3}/m | |
177–182 | 622 | D_{6} | 226 | [2,6]^{+} | 12 | P622, P6_{1}22, P6_{5}22, P6_{2}22, P6_{4}22, P6_{3}22 | |
183–186 | 6mm | C_{6v} | *66 | [6] | 12 | P6mm, P6cc, P6_{3}cm, P6_{3}mc | |
187–190 | 6m2 | D_{3h} | *223 | [2,3] | 12 | P6m2, P6c2, P62m, P62c | |
191–194 | 6/mmm | D_{6h} | *226 | [2,6] | 24 | P6/mmm, P6/mcc, P6_{3}/mcm, P6_{3}/mmc | |
195–199 | Cubic (36) |
23 | T | 332 | [3,3]^{+} | 12 | P23, F23, I23 P2_{1}3, I2_{1}3 |
200–206 | m3 | T_{h} | 3*2 | [3^{+},4] | 24 | Pm3, Pn3, Fm3, Fd3, Im3, Pa3, Ia3 | |
207–214 | 432 | O | 432 | [3,4]^{+} | 24 | P432, P4_{2}32 F432, F4_{1}32 I432 P4_{3}32, P4_{1}32, I4_{1}32 | |
215–220 | 43m | T_{d} | *332 | [3,3] | 24 | P43m, F43m, I43m P43n, F43c, I43d | |
221–230 | m3m | O_{h} | *432 | [3,4] | 48 | Pm3m, Pn3n, Pm3n, Pn3m Fm3m, Fm3c, Fd3m, Fd3c Im3m, Ia3d |
Note. An e plane is a double glide plane, one having glides in two different directions. They are found in seven orthorhombic, five tetragonal and five cubic space groups, all with centered lattice. The use of the symbol e became official with Hahn (2002).
The lattice system can be found as follows. If the crystal system is not trigonal then the lattice system is of the same type. If the crystal system is trigonal, then the lattice system is hexagonal unless the space group is one of the seven in the rhombohedral lattice system consisting of the 7 trigonal space groups in the table above whose name begins with R. (The term rhombohedral system is also sometimes used as an alternative name for the whole trigonal system.) The hexagonal lattice system is larger than the hexagonal crystal system, and consists of the hexagonal crystal system together with the 18 groups of the trigonal crystal system other than the seven whose names begin with R.
The Bravais lattice of the space group is determined by the lattice system together with the initial letter of its name, which for the non-rhombohedral groups is P, I, F, or C, standing for the principal, body centered, face centered, or C-face centered lattices.
The 233rd Space Group (233rd SG) is a unit of the Colorado Air National Guard located at Greeley Air National Guard Station, Greeley. The 233rd Space Group provides immediate, worldwide missile warning, space launch and detection in the event of an attack against the United States. If activated to federal service, the Wing is gained by the United States Air Force Space Command.
310th Space WingThe 310th Space Wing is an Air Reserve Component (ARC) of the United States Air Force. It is assigned to the Tenth Air Force, Air Force Reserve Command, stationed at Schriever Air Force Base, Colorado.
The 310th SW is mission partnered with the 21st Space Wing, Air Force Space Command (AFSPC), 30th Space Wing, (AFSPC), 50th Space Wing, (AFSPC) and 460th Space Wing, (AFSPC). If mobilized, the wing is gained by AFSPC.
73rd Space GroupThe 73d Space Group is an inactive United States Air Force space surveillance organization. Its last assignment was with Fourteenth Air Force, being stationed at Falcon Air Force Base, Colorado. It was inactivated on 26 April 1995.
The Group performed space surveillance. In April 1995 the 73d Space Surveillance Group merged with the 21st Space Wing. From that point the 21st became the largest wing in the United States Air Force with units deployed literally throughout the world.
Antimony triselenideAntimony triselenide is the chemical compound with the formula Sb2Se3. The material exists as the sulfosalt mineral antimonselite, which crystallizes in an orthorhombic space group. In this compound, antimony has the oxidation state +3 and selenium −2, but in fact the bonding in this compound is highly covalent as reflected by the black color and semiconducting properties of this and related materials.It may be formed by the reaction of antimony with selenium.
AvogadriteAvogadrite ((K,Cs)BF4) is a potassium-caesium tetrafluoroborate in the halide class. Avogadrite crystallizes in the orthorhombic system (space group Pnma) with cell parameters a 8.66 Å, b 5.48 Å and c Å 7.03.
Convex uniform honeycombIn geometry, a convex uniform honeycomb is a uniform tessellation which fills three-dimensional Euclidean space with non-overlapping convex uniform polyhedral cells.
Twenty-eight such honeycombs are known:
the familiar cubic honeycomb and 7 truncations thereof;
the alternated cubic honeycomb and 4 truncations thereof;
10 prismatic forms based on the uniform plane tilings (11 if including the cubic honeycomb);
5 modifications of some of the above by elongation and/or gyration.They can be considered the three-dimensional analogue to the uniform tilings of the plane.
The Voronoi diagram of any lattice forms a convex uniform honeycomb in which the cells are zonohedra.
Cubic crystal systemIn crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of these crystals:
Primitive cubic (abbreviated cP and alternatively called simple cubic)
Body-centered cubic (abbreviated cI or bcc),
Face-centered cubic (abbreviated cF or fcc, and alternatively called cubic close-packed or ccp)Each is subdivided into other variants listed below. Note that although the unit cell in these crystals is conventionally taken to be a cube, the primitive unit cell often is not.
Cubic honeycombThe cubic honeycomb or cubic cellulation is the only proper regular space-filling tessellation (or honeycomb) in Euclidean 3-space, made up of cubic cells. It has 4 cubes around every edge, and 8 cubes around each vertex. Its vertex figure is a regular octahedron. It is a self-dual tessellation with Schläfli symbol {4,3,4}. John Horton Conway calls this honeycomb a cubille.
A geometric honeycomb is a space-filling of polyhedral or higher-dimensional cells, so that there are no gaps. It is an example of the more general mathematical tiling or tessellation in any number of dimensions.
Honeycombs are usually constructed in ordinary Euclidean ("flat") space, like the convex uniform honeycombs. They may also be constructed in non-Euclidean spaces, such as hyperbolic uniform honeycombs. Any finite uniform polytope can be projected to its circumsphere to form a uniform honeycomb in spherical space.
Eudialyte groupEudialyte group is a group of complex trigonal zircono- and, more rarely, titanosilicate minerals with general formula [N(1)N(2)N(3)N(4)N(5)]3[M(1a)M(1b)]3M(2)3M(4)Z3[Si24O72]O'4X2, where N(1) and N(2) and N(3) and N(5) = Na+ and more rarely H3O+ or H2O, N(4) = Na+, Sr2+, Mn2+ and more rarely H3O+ or H2O or K+ or Ca2+ or REE3+ (rare earth elements), M(1) and M(1b) = Ca2+, M(1a) = Ca2+ or Mn2+ or Fe2+, M(2) = Fe (both II and III), Mn and rarely Na+, K+ or Zr4+, M(3) = Si, Nb and rarely W, Ti and [] (vacancy), M(4) = Si and or rarely [], Z Zr4+ and or rarely Ti4+, and X = OH−, Cl− and more rarely CO32− or F−. Some of the eudialyte-like structures can even be more complex, however, in general, its typical feature is the presence of [Si3O9]6− and [Si9O27]18− ring silicate groups. Space group is usually R3m or R-3m but may be reduced to R3 due to cation ordering. Like other zirconosilicates, the eudialyte group minerals possess alkaline ion-exchange properties, as microporous materials.
GarnetGarnets ( ) are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series: pyrope-almandine-spessartine and uvarovite-grossular-andradite.
Hexagonal crystal familyIn crystallography, the hexagonal crystal family is one of the 6 crystal families, which includes 2 crystal systems (hexagonal and trigonal) and 2 lattice systems (hexagonal and rhombohedral).
The hexagonal crystal family consists of the 12 point groups such that at least one of their space groups has the hexagonal lattice as underlying lattice, and is the union of the hexagonal crystal system and the trigonal crystal system. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral.
Monoclinic crystal systemIn crystallography, the monoclinic crystal system is one of the 7 crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic system. They form a rectangular prism with a parallelogram as its base. Hence two vectors are perpendicular (meet at right angles), while the third vector meets the other two at an angle other than 90°.
Orthorhombic crystal systemIn crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base (a by b) and height (c), such that a, b, and c are distinct. All three bases intersect at 90° angles, so the three lattice vectors remain mutually orthogonal.
Space Innovation and Development CenterThe Space Innovation & Development Center (SIDC), formerly the Space Warfare Center (SWC), was a military unit of the United States Air Force. It was directly under Air Force Space Command (AFSPC) and resided at Schriever Air Force Base, Colorado. In 2013, AFSPC and ACC restructured the SIDC. Effective 1 April 2013, the SIDC transitioned into several Operating Locations at Schriever AFB under ACC's United States Air Force Warfare Center, headquartered at Nellis Air Force Base, NV.The SIDC aimed to "unlock the potential" as premier innovators, integrators and operational testers of air, space and cyberspace power to the warfighter. The center's mission was to advance full-spectrum warfare through rapid innovation, integration, training testing, and experimentation.
StibniteStibnite, sometimes called antimonite, is a sulfide mineral with the formula Sb2S3. This soft grey material crystallizes in an orthorhombic space group. It is the most important source for the metalloid antimony. The name is from the Greek στίβι stibi through the Latin stibium as the old name for the mineral and the element antimony.
Tin(II) sulfideTin(II) sulfide is a chemical compound of tin and sulfur. The chemical formula is SnS. Its natural occurrence concerns herzenbergite (α-SnS), a rare mineral. At elevated temperatures above 905K, SnS undergoes a second order phase transition to β-SnS (space group: cmcm, No. 63). in recent years, it has become evident that a new polymorph of SnS exist based upon the cubic crystal system, π-SnS (space group: P213, No. 198).
Triclinic crystal systemIn crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. In addition, the angles between these vectors must all be different and may include 90°.
The triclinic lattice is the least symmetric of the 14 three-dimensional Bravais lattices. It has (itself) the minimum symmetry all lattices have: points of inversion at each lattice point and at 7 more points for each lattice point: at the midpoints of the edges and the faces, and at the center points. It is the only lattice type that itself has no mirror planes.
Zirconium tetrafluorideZirconium(IV) fluoride (ZrF4) is an inorganic chemical compound. It is a component of ZBLAN fluoride glass. It is insoluble in water. It is the main component of fluorozirconate glasses.
Three crystalline phases of ZrF4 have been reported, α (monoclinic), β (tetragonal, Pearson symbol tP40, space group P42/m, No 84) and γ (unknown structure). β and γ phases are unstable and irreversibly transform into the α phase at 400 °C.Zirconium fluoride is used as a zirconium source in oxygen-sensitive applications, e.g. metal production. Zirconium fluoride can be purified by distillation or sublimation.Conditions/substances to avoid are: moisture, active metals, acids and oxidizing agents.
Zirconium fluoride in a mixture with other fluorides is a coolant for molten salt reactors. In the mixture with sodium fluoride it is a candidate coolant for the Advanced High-Temperature Reactor.
Together with uranium salt, zirconium fluoride can be a component of fuel-coolant in molten salt reactors. Mixture of sodium fluoride, zirconium fluoride, and uranium tetrafluoride (53-41-6 mol.%) was used as a coolant in the Aircraft Reactor Experiment. A mixture of lithium fluoride, beryllium fluoride, zirconium fluoride, and uranium-233 tetrafluoride was used in the Molten-Salt Reactor Experiment. (Uranium-233 is used in the thorium fuel cycle reactors.)
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