Term
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Definition
| The possibility of the existence of two or more different crystal structures for a substance (generally an elemental solid). |
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Term
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Definition
Having a noncrystalline
structure. |
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Term
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Definition
| Exhibiting different values of a property in different crystallographic directions. |
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Term
| atomic packing factor (APF) |
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Definition
| The fraction of the volume of a unit cell that is occupied by "hard sphere" atoms or ions. |
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Term
| body-centered cubic (BCC) |
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Definition
| A common crystal structure found in some elemental metals. Within the cubic unit cell, atoms are located at corner and cell center positions. |
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Term
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Definition
| A relationship that stipulates the condition for diffraction by a set of crystallographic planes. |
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Term
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Definition
| The number of atomic or ionic nearest neighbors. |
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Term
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Definition
| The state of a solid material characterized by a periodic and repeating three-dimensional array of atoms, ions, or molecules. |
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Term
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Definition
| For crystalline materials, the manner in which atoms or ions are arranged in space. It is defined in terms of the unit cell geometry and the atom positions within the unit cell. |
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Term
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Definition
| A scheme by which crystal structures are classified according to unit cell geometry. This geometry is specified in terms of the relationships between edge lengths and interaxial angles. There are seven different crystal systems. |
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Term
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Definition
| Constructive interference of x-ray beams that are scattered by atoms of a crystal. |
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Term
| face-centered cubic (FCC) |
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Definition
| A crystal structure found in some of the common elemental metals. Within the cubic unit cell, atoms are located at all corner and face-centered positions. |
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Term
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Definition
| An individual crystal in a polycrystalline metal or ceramic. |
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Term
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Definition
| The interface separating two adjoining grains having different crystallographic orientations. |
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Term
| hexagonal close-packed (HCP) |
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Definition
| A crystal structure found for some metals. The HCP unit cell is of hexagonal geometry and is generated by the stacking of close-packed planes of atoms. |
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Term
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Definition
| Having identical values of a property in all crystallographic directions. |
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Term
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Definition
| The regular geometrical arrangement of points in crystal space. |
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Term
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Definition
| The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry. |
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Term
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Definition
| A set of three integers (four for hexagonal) that designate crystallographic planes, as determined from reciprocals of fractional axial intercepts. |
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Term
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Definition
| The solid state wherein there is no long-range atomic order. Sometimes the terms amorphous, glassy, and vitreous are used synonymously. |
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Term
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Definition
| Refers to crystalline materials that are composed of more than one crystal or grain. |
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Term
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Definition
| The ability of a solid material to exist in more than one form or crystal structure. |
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Term
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Definition
| A crystalline solid for which the periodic and repeated atomic pattern extends throughout its entirety without interruption. |
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Term
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Definition
| The basic structural unit of a crystal structure. It is generally defined in terms of atom (or ion) positions within a parallelepiped volume. |
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