Interstitial sites in simple cubic and close-packed structures
The holes are easy to see if you try to pack circles together; no matter how close you get them or how you arrange them, you will have empty space in between. The same is true in a unit cell; no matter how the atoms are arranged, there will be interstitial sites present between the atoms. These sites or holes can be filled with other atoms (interstitial defect). The picture with packed circles is only a 2D representation. In a crystal lattice, the atoms (spheres) would be packed in a 3D arrangement. This results in different shaped interstitial sites depending on the arrangement of the atoms in the lattice.
Octahedral (red) and tetrahedral (blue) interstitial symmetry polyhedra in a face-centered cubic lattice. The actual interstitial atom would ideally be in the middle of one of the polyhedra.
A close packed unit cell, both face-centered cubic and hexagonal close packed, can form two different shaped holes. Looking at the three green spheres in the hexagonal packing illustration at the top of the page, they form a triangle-shaped hole. If an atom is arranged on top of this triangular hole it forms a tetrahedral interstitial hole. If the three atoms in the layer above are rotated and their triangular hole sits on top of this one, it forms an octahedral interstitial hole.[citation needed] In a close-packed structure there are 4 atoms per unit cell and it will have 4 octahedral voids (1:1 ratio) and 8 tetrahedral voids (1:2 ratio) per unit cell.[1] The tetrahedral void is smaller in size and could fit an atom with a radius 0.225 times the size of the atoms making up the lattice. An octahedral void could fit an atom with a radius 0.414 times the size of the atoms making up the lattice.[1] An atom that fills this empty space could be larger than this ideal radius ratio, which would lead to a distorted lattice due to pushing out the surrounding atoms, but it cannot be smaller than this ratio.[1]
If half of the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the zincblende crystal structure. If all the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the fluorite structure or antifluorite structure. If all the octahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the rock-salt structure.
If half of the tetrahedral sites of the parent HCP lattice are filled by ions of opposite charge, the structure formed is the wurtzite crystal structure. If all the octahedral sites of the anion HCP lattice are filled by cations, the structure formed is the nickel arsenide structure.
Simple cubicedit
A simple cubic unit cell, with stacks of atoms arranged as if at the eight corners of a cube would form a single cubic hole or void in the center. If these voids are occupied by ions of opposite charge from the parent lattice, the cesium chloride structure is formed.
Body-centered cubic (BCC)edit
A body-centered cubic unit cell has six octahedral voids located at the center of each face of the unit cell, and twelve further ones located at the midpoint of each edge of the same cell, for a total of six net octahedral voids. Additionally, there are 24 tetrahedral voids located in a square spacing around each octahedral void, for a total of twelve net tetrahedral voids. These tetrahedral voids are not local maxima and are not technically voids, but they do occasionally appear in multi-atom unit cells.
An interstitial defect refers to additional atoms occupying some interstitial sites at random as crystallographic defects in a crystal which normally has empty interstitial sites by default.
Referencesedit
^ abc"Study of Interstitial Voids". from the original on 2020-08-04.
January 01, 1970
interstitial, site, crystallography, interstitial, sites, holes, voids, empty, space, that, exists, between, packing, atoms, spheres, crystal, structure, citation, needed, simple, cubic, close, packed, structures, holes, easy, pack, circles, together, matter, . In crystallography interstitial sites holes or voids are the empty space that exists between the packing of atoms spheres in the crystal structure citation needed Interstitial sites in simple cubic and close packed structures The holes are easy to see if you try to pack circles together no matter how close you get them or how you arrange them you will have empty space in between The same is true in a unit cell no matter how the atoms are arranged there will be interstitial sites present between the atoms These sites or holes can be filled with other atoms interstitial defect The picture with packed circles is only a 2D representation In a crystal lattice the atoms spheres would be packed in a 3D arrangement This results in different shaped interstitial sites depending on the arrangement of the atoms in the lattice Contents 1 Close packed 1 1 Face centered cubic FCC 1 2 Hexagonal close packed HCP 2 Simple cubic 3 Body centered cubic BCC 4 Interstitial defect 5 ReferencesClose packed edit nbsp Octahedral red and tetrahedral blue interstitial symmetry polyhedra in a face centered cubic lattice The actual interstitial atom would ideally be in the middle of one of the polyhedra A close packed unit cell both face centered cubic and hexagonal close packed can form two different shaped holes Looking at the three green spheres in the hexagonal packing illustration at the top of the page they form a triangle shaped hole If an atom is arranged on top of this triangular hole it forms a tetrahedral interstitial hole If the three atoms in the layer above are rotated and their triangular hole sits on top of this one it forms an octahedral interstitial hole citation needed In a close packed structure there are 4 atoms per unit cell and it will have 4 octahedral voids 1 1 ratio and 8 tetrahedral voids 1 2 ratio per unit cell 1 The tetrahedral void is smaller in size and could fit an atom with a radius 0 225 times the size of the atoms making up the lattice An octahedral void could fit an atom with a radius 0 414 times the size of the atoms making up the lattice 1 An atom that fills this empty space could be larger than this ideal radius ratio which would lead to a distorted lattice due to pushing out the surrounding atoms but it cannot be smaller than this ratio 1 Face centered cubic FCC edit Further information Cubic crystal system Multi element structures If half of the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge the structure formed is the zincblende crystal structure If all the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge the structure formed is the fluorite structure or antifluorite structure If all the octahedral sites of the parent FCC lattice are filled by ions of opposite charge the structure formed is the rock salt structure Hexagonal close packed HCP edit Further information Hexagonal crystal family Multi element structures If half of the tetrahedral sites of the parent HCP lattice are filled by ions of opposite charge the structure formed is the wurtzite crystal structure If all the octahedral sites of the anion HCP lattice are filled by cations the structure formed is the nickel arsenide structure Simple cubic editA simple cubic unit cell with stacks of atoms arranged as if at the eight corners of a cube would form a single cubic hole or void in the center If these voids are occupied by ions of opposite charge from the parent lattice the cesium chloride structure is formed Body centered cubic BCC editA body centered cubic unit cell has six octahedral voids located at the center of each face of the unit cell and twelve further ones located at the midpoint of each edge of the same cell for a total of six net octahedral voids Additionally there are 24 tetrahedral voids located in a square spacing around each octahedral void for a total of twelve net tetrahedral voids These tetrahedral voids are not local maxima and are not technically voids but they do occasionally appear in multi atom unit cells Interstitial defect editMain article Interstitial defect An interstitial defect refers to additional atoms occupying some interstitial sites at random as crystallographic defects in a crystal which normally has empty interstitial sites by default References edit a b c Study of Interstitial Voids Archived from the original on 2020 08 04 Retrieved from https en wikipedia org w index php title Interstitial site amp oldid 1222710067, wikipedia, wiki, book, books, library,
