(See related pages)
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| Crystal | a solid composed of atoms, ions, or molecules arranged in a pattern that is
repeated in three dimensions. (See page(s) 108, Sec. 3.1) |
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| Crystal structure | a regular three-dimensional pattern of atoms or ions in space. (See page(s) 108, Sec. 3.1) |
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| Space lattice | a three-dimensional array of points each of which has identical
surroundings. (See page(s) 108, Sec. 3.1) |
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| Lattice point | one point in an array in which all the points have identical
surroundings. (See page(s) 108, Sec. 3.1) |
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| Unit cell | a convenient repeating unit of a space lattice. The axial lengths and axial
angles are the lattice constants of the unit cell. (See page(s) 108, Sec. 3.1) |
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| Body-centered cubic (BCC) unit cell | a unit cell with an atomic packing arrangement
in which one atom is in contact with eight identical atoms located at the corners of an
imaginary cube. (See page(s) 108, Sec. 3.3) |
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| Face-centered cubic (FCC) unit cell | a unit cell with an atomic packing arrangement
in which 12 atoms surround a central atom. The stacking sequence of layers of close-packed
planes in the FCC crystal structure is ABCABC. . . . (See page(s) 108, Sec. 3.3) |
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| Hexagonal close-packed (HCP) unit cell | a unit cell with an atomic packing
arrangement in which 12 atoms surround a central identical atom. The stacking
sequence of layers of close-packed planes in the HCP crystal structure is
ABABAB. . . . (See page(s) 108, Sec. 3.3) |
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| Atomic packing factor (APF) | the volume of atoms in a selected unit cell divided by
the volume of the unit cell. (See page(s) 108, Sec. 3.3) |
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| Indices of direction in a cubic crystal | a direction in a cubic unit cell is indicated by a
vector drawn from the origin at one point in a unit cell through the surface of the unit
cell; the position coordinates (x, y, and z) of the vector where it leaves the surface of
the unit cell (with fractions cleared) are the indices of direction. These indices,
designated u, v , and w are enclosed in brackets as [uvw]. Negative indices are
indicated by a bar over the index. (See page(s) 108, Sec. 3.5) |
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| Indices for cubic crystal planes (Miller indices) | the reciprocals of the intercepts
(with fractions cleared) of a crystal plane with the x, y, and z axes of a unit cube are
called the Miller indices of that plane. They are designated h, k, and l for the x, y, and
z axes, respectively, and are enclosed in parentheses as (hkl). Note that the selected
crystal plane must not pass through the origin of the x, y, and z axes. (See page(s) 108, Sec. 3.6) |
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| Volume density | ρv: mass per unit volume; this quantity is usually expressed in Mg/m3
or g/cm3 . (See page(s) 108, Sec. 3.9) |
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| Planar density | ρp: the equivalent number of atoms whose centers are intersected by a
selected area divided by the selected area. (See page(s) 108, Sec. 3.9) |
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| Linear density | ρt: the number of atoms whose centers lie on a specific direction on a
specific length of line in a unit cube. (See page(s) 108, Sec. 3.9) |
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| Polymorphism (as pertains to metals) | the ability of a metal to exist in two or more
crystal structures. For example, iron can have a BCC or an FCC crystal structure,
depending on the temperature. (See page(s) 109, Sec. 3.10) |