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Topic: Crystal lattice

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	Crystal Lattice Structures
		Fluorite Structure - The structure of the mineral fluorite (calcium fluoride) may be viewed as a CCP lattice of cations (Z = 4), with the smaller anion occupying all of the Td holes (Z = 8).
		The Td cavities reside on a SC lattice which is half the dimension of the CCP lattice.
		Zinc Blende lattices - The lattice of cations in zinc blende is a FCC lattice of the same dimension as the anion lattice, so the structure can be described as interpenetrating FCC lattices of the same unit cell dimension.
	members.kr.inter.net /joo/physics/curri-sub/crystal/lattice.html (1058 words)

	Photonic lattice
		The lattice, dubbed a photonic crystal (crystals have regularly repeating internal structures), now works in the infrared range (approximately 10-micron wavelengths).
		The nearly leak-proof lattices form a cage that trap and guide approximately 95 percent of the light sent within them, as compared with approximately 30 percent for conventional waveguides, and they take only one-tenth to one-fifth the space to bend the light.
		Gears that spin require spaces between parts; specifically, a silicon base is covered with an expendable coating in which a part can be etched, and then the expendable portion is removed by chemical and mechanical means, leaving the gear or axle unencumbered by surrounding material and thus able to spin freely [http://mems.sandia.gov/scripts/].
	www.sandia.gov /media/photonic.htm (1240 words)

	Vibrations in crystal lattice play big role in high temperature superconductors
		The pairing is made possible by interactions between the electrons and the metal atoms vibrating in place in the crystal lattice.
		The experiment, which involved tweaking the material's crystal lattice by substituting heavier oxygen-18 for some of the normal oxygen-16, showed that a heavier and thus stiffer lattice affected the electron cloud that permeates the superconductor.
		The crystal structure is basically comprised of two alternating layers: one a plane of copper and oxygen molecules interspersed with strontium and calcium atoms, the other a lattice of bismuth and oxygen.
	www.physlink.com /News/081704Supercomductors.cfm (1127 words)

	Crystal Lattice Structures
		This lattice is "closest packed", because spheres of equal size occupy the maximum amount of space in this arrangment (74.05%); since this closest packing is based on a cubic array, it is called "cubic closest packing": CCP = FCC.
		Rhombohedral (R) lattice - If, in the (ABC) layered lattice, the interplanar spacing is not the closest packed value (1.633r), then the primitive (Z = 1) unit cell is a rhombohedron with a = b = c <> 2r and alpha = beta = gamma <> 60 degrees.
		Zinc Blende lattices - The lattice of cations in zinc blende is a FCC lattice of the same dimension as the anion lattice, so the structure can be described as interpenetrating FCC lattices of the same unit cell dimension.
	www.chem.lsu.edu /htdocs/people/sfwatkins/ch4570/lattices/lattice.html (1147 words)

	08.16.2004 - Vibrations in crystal lattice plays big role in high temperature superconductors
		The complex crystal structure of Bi-2212, a typical cuprate ceramic high temperature superconductor, showing two distinct alternating layers: the copper oxide layer (purple is copper, brown is oxygen) and the bismuth oxide layer (green is bismuth), interspersed with atoms of calcium (pink) and strontium (orange).
		The experiment, which involved tweaking the material's crystal lattice by substituting heavier oxygen-18 for some of the normal oxygen-16, showed that a heavier and thus stiffer lattice affected the electron cloud that permeates the superconductor.
		The crystal structure is basically comprised of two alternating layers: one a plane of copper and oxygen molecules interspersed with strontium and calcium atoms, the other a lattice of bismuth and oxygen.
	www.berkeley.edu /news/media/releases/2004/08/16_Lanzara.shtml (1181 words)

	Description of Crystal Lattices (Site not responding. Last check: )
		The existence of the crystal lattice implies a degree of symmetry in the arrangement of the lattice, and the existing symmetries have been studied extensively.
		Treating the lattice vibrations quantum mechanically led to the Einstein model and the Debye model of specific heat.
		Lattice vibrations can also interact with light to produce scattering called Brillouin scattering, which is used in laser spectroscopy.
	hyperphysics.phy-astr.gsu.edu /hbase/solids/lattice.html (202 words)

	Crystal Morphology, Crystal Symmetry, Crystallographic Axes
		The symmetry observed in crystals as exhibited by their crystal faces is due to the ordered internal arrangement of atoms in a crystal structure, as mentioned previously.
		Thus, in imperfect crystals or distorted crystals where the lengths of the edges or faces of symmetry related faces are not equal, the symmetry can still be determined by the angles between the faces.
		Depending on the symmetry of the lattice, the directions may or may not be perpendicular to one another, and the divisions along the coordinate axes may or may not be equal along the axes.
	www.tulane.edu /~sanelson/eens211/crystalmorphology&symmetry.htm (1140 words)

	Crystalline Structures \| Crystal Lattice \| Crystal System
		The unit cell is determined by its lattice parameters, the length of the cell edges and the angles between them, while the positions of the atoms inside the unit cell are described by the set of atomic positions (xi,yi,zi) measured from a lattice point.
		The crystal system is a grouping of crystal structures that are categorized according to the axial system used to describe their "lattice".
		A crystal's lattice is a three dimensional network of atoms that are arranged in a symmetrical pattern.
	www.khulsey.com /jewelry/crystalline_structures.html (753 words)

	Intro to Minerals: Crystal Class and System
		For example, crystals of the holomorphic class of the isometric system possess inversion symmetry, three 4-fold axes of rotational symmetry, the characteristic set of four 3-fold axes of rotational symmetry which is indicative of the isometric crystal system, six 2-fold axes of rotational symmetry, and nine different mirror planes.
		The rhombic pyramidal crystal class is thus a member of the orthorhombic crystal system, the tetragonal pyramidal class is a member of the tetragonal crystal system, and the trigonal and hexagonal pyramidal classes are members of the rhombohedral (trigonal) and hexagonal divisions of the hexagonal crystal system respectively.
		It is thus apparent that the characteristic symmetry element of the isometric crystal system is the possession of four 3-fold axes of rotational symmetry, while the characteristic symmetry element of the rhombohedral division of the hexagonal crystal system is the possession of a single 3-fold axis of rotational symmetry.
	dave.ucsc.edu /myrtreia/crystal.html (4278 words)

	How it Works : Crystal (Site not responding. Last check: )
		Those crystals which do exist in near perfection, such as diamonds, must be cut to show the crystal faces of the gems to their full effect.
		The crystal grows by the addition of new material until an equilibrium is reached when the rate of deposition of material equals the rate at which the crystal is dissolved into the surrounding medium.
		The crystal shape depends upon the temperature at which the crystals were formed and upon the speed of their formation.
	www.triquartz.co.uk /crystal.html (2438 words)

	crystal lattice - HighBeam Encyclopedia (Site not responding. Last check: )
		The lattice is divided into a number of identical blocks or cells that are repeated in all directions to form a geometric pattern.
		Lattices are classified according to their dominant symmetries: isometric, trigonal, hexagonal, tetragonal, orthorhombic, monoclinic, and triclinic.
		Lattice symmetry and identification - the fundamental role of reduced cells in materials characterization.
	www.encyclopedia.com /doc/1B1-361971.html (491 words)

	Internal Structure of Crystals I
		A crystal turns out to be made from the regular stacking of a building block (without turning it while stacking) having certain proportions of the length of its edges.
		A lattice is, therefore, an imaginary pattern of points (or nodes) in which every point (node) has an environment that is identical to that of any other point (node) in the pattern.
		We could say that the two-dimensional patterns, involved in two-dimensional crystals, are representations of the corresponding groups (which are the main mathematical entities in group theory), and these representations are examined analytically, which means that the mentioned patterns are as such given, and what we do is to examine the symmetries inherent in those patterns.
	home.hetnet.nl /~heackel/d2_lattice_1.html (4755 words)

	Program_speaker_dawson
		Since the crystal is formed with repeating unit cells, it logically follows that there will be some symmetry in the arrangement of the crystal lattice.
		For example, on a given crystal plane, the bond strength between the atoms on either side of the plane may be weak.
		Using his crystal props again, Dr. Dawson showed how the directions for cleavage formed along the flat surfaces, where the individual atoms were at their greatest distance from one another.
	www.attawaygems.com /NMFG/Program_speaker_dawson.html (1144 words)

	News \| TimesDaily.com \| TimesDaily \| Florence, AL (Site not responding. Last check: )
		A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way; which is periodically repeated in three dimensions on a lattice.
		The crystal systems are a grouping of crystal structures according to the axial system used to describe their lattice.
		The space group of the crystal structure is composed of the translational symmetry operations in addition to the operations of the point group.
	www.timesdaily.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=crystalline_structure (1162 words)

	Crystal Structure Databases
		The crystal structure information includes mineral name, specification, crystal chemical formula, space group, unit cell parameters, coordinates, thermal factors and occupancy of atomic positions as well as literature references on crystal structure determination.
		This database is a sister to the American Mineralogist Crystal Structure Database (AMCSD) and contains all the data that is in the AMCSD as well as data that has been deposited by individuals and laboratories.
		Crystal structure data are downloadable in CIF format, and users may upload crystal data as CIF or REF files.
	serc.carleton.edu /research_education/crystallography/xldatabases.html (457 words)

	goniometry of direct lattice vectors and direct crystallographic analyses
		The relative orientation of the crystals to be analyzed with respect to the electron microscope is given by a 3 by 3 matrix i.e.
		In recent years, a method for the structural analysis of powders of nanometer sized cubic crystals has been developed on the basis of goniometry of direct lattice vectors by means of high resolution phase contrast imaging [21-28].
		My graduate students and I will implement direct crystallographic analyses on the basis of goniometry of direct lattice vectors at the TEM of PSU because the convergent beam electron diffraction (CBED) technique is not well suited to the analysis of the structure of self assembled and colloidal semiconductor quantum dots and other crystalline nanoparticles.
	www.physics.pdx.edu /~pmoeck/goniometry.htm (2503 words)

	Lattice and Crystal
		An ideal crystal is a repetition of identical structural units in three dimensional space.
		The periodicity is described by a mathematical lattice (which are mathematical points at specific coordinates in space), the identical structural units (or base of the crystal) are the atoms in some specific arrangement which are unambiguously placed at every lattice point.
		Whereas, for example, it shows best the cubic symmetry of the cubic lattices, its elementary cell is not a primitive unit cell of the lattice, i.e.
	www.tf.uni-kiel.de /matwis/amat/def_en/kap_1/basics/b1_3_1.html (381 words)

	Cerius² Builders - Crystal Builder
		Crystal structures are of fundamental importance in materials science.
		The initial orientation of the crystal is such that the c axis of the cell is perpendicular to the screen and the projection of the b axis on the screen is vertical (Figure 1).
		The number of unit cells of the crystal that are displayed is a display property only--that is, all calculations on a crystal model are done using periodic boundary conditions and assuming an infinitely repeating lattice.
	www.chem.cmu.edu /courses/09-560/docs/msi/builder/3_Crystal.html (5095 words)

	Crystals and Lattices
		The perfection of a lattice is disturbed by lattice vibrations (phonons), which have observable effects on microscopic properties, such as X-ray diffraction, as well as by impurities and lattice defects such as dislocations.
		In terms of the reciprocal lattice, let n be a unit vector in the direction of the incident radiation, and n' a unit vector in the direction of the diffracted beam.
		That of a face-centered cubic lattice is a truncated octahedron.
	www.du.edu /~jcalvert/phys/lattice.htm (6338 words)

	Explore Whipple Collections - Crystal lattice models (Site not responding. Last check: )
		A crystal lattice is a repeating pattern of atoms in a solid.
		This crystal lattice model (Image 1) shows the distances between atoms of manganese and their geometrical arrangement within the crystal structure.
		When metallic manganese is heated the crystal lattice undergoes changes in its structure before the metal melts.
	www.hps.cam.ac.uk /whipple/explore/models/modellingchemistry/crystallatticemodels (485 words)

	Chemical Lattice Types
		Only when the lattice (initially a point lattice, but later provided with motifs to give the Space Group) is provided with the actual chemical units, we have to do with the actual complete internal STRUCTURE of the given (single) crystal.
		The Structure of a crystal is equivalent to the nature of its constituents and their actual spatial arrangement, including the absolute distances between those constituents.
		If we imagine a crystal to be indefinitely extended in space, then crystals exhibit several translational symmetries, meaning that when we subject it to certain translational operations, then the result is a coincidence of the (internal) crystal pattern before and after the operation.
	home.hetnet.nl /~turing/chemical_lattice_1.html (1099 words)

	crystal lattice definition - Dictionary - MSN Encarta
		crystal lattice definition - Dictionary - MSN Encarta
		Search for "crystal lattice" in all of MSN Encarta
		array of components in crystal: the regular array of points in space that are occupied by the atoms, ions, or molecules that make up a crystal
	encarta.msn.com /dictionary_1861688655/crystal_lattice.html (89 words)

	Giant Ionic Lattice
		But the crystal still holds together and sodium chloride has a high melting point of 801 °C. The electrostatic forces of attraction between oppositely-charged ions must exceed the repulsions between ions of the same charge.
		In a crystal lattice, ionic bonding extends throughout the entire structure.
		You could think of the sodium chloride crystal as a lattice of Cl ions with the smaller Na ions filling the holes between them.
	www.avogadro.co.uk /structure/chemstruc/ionic/g-ionic.htm (734 words)

	The MOE Crystal Builder (Site not responding. Last check: )
		The absolute positions of the points of a lattice, and hence the unit cell, are arbitrary with respect to a pattern.
		Lattices can be classified into "systems", each system being characterized by the shape of its associated unit cell.
		When a crystal unit cell is being built and edited, other atoms not implicated in the crystal may exist concurrently in the system.
	www.chemcomp.com /feature/crysbld.htm (1784 words)

	Introduction to Cubic Crystal Lattice Structures
		The unit cell can be thought of as a box which when stacked together in 3-dimensions produces the crystal lattice.
		In the cubic crystal system three types of arrangements are found;
		Ionic crystals are composed of charged species and the ions of the compound have different sizes.
	www.okstate.edu /jgelder/solstate.html (538 words)

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