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In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms, ions or molecules in a crystalline liquid or solid.〔Solid State Physics (2nd Edition), J.R. Hook, H.E. Hall, Manchester Physics Series, John Wiley & Sons, 2010, ISBN 978-0-471-92804-1〕 It describes a highly ordered structure, occurring due to the intrinsic nature of its constituents to form symmetric patterns. The Box can be thought of as an array of 'small boxes' infinitely repeating in all three spatial directions. Such a unit cell is the smallest unit of volume that contains all of the structural and symmetry information to build-up the macroscopic structure of the lattice by translation. Patterns are located upon the points of a lattice, which is an array of points repeating periodically in three dimensions. The lengths of the edges of a unit cell and the angles between them are called the ''lattice parameters.'' The symmetry properties of the crystal are embodied in its space group.〔 A crystal's structure and symmetry play a role in determining many of its physical properties, such as cleavage, electronic band structure, and optical transparency. == Unit cell == The crystal structure of a material (the arrangement of atoms within a given type of crystal) can be described in terms of its unit cell. The unit cell is a small box containing one or more atoms arranged in 3-dimensions. The unit cells stacked in three-dimensional space describe the bulk arrangement of atoms of the crystal. The unit cell is represented in terms of its lattice parameters, which are the lengths of the cell edges (a,b and c) and the angles between them (alpha, beta and gamma), 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. Commonly, atomic positions are represented in terms of fractional coordinates, relative to the unit cell lengths. Image:Lattic_simple_cubic.svg|Simple cubic (P) Image:Lattice_body_centered_cubic.svg|Body-centered cubic (I) Image:Lattice_face_centered_cubic.svg|Face-centered cubic (F) The atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell. This does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the space group of the crystal structure, and this is usually a black box operation performed by computer programs. However, manual calculation of the atomic positions within the unit cell can be performed from the asymmetric unit, through the application of the symmetry operators described within the 'International Tables for Crystallography: Volume A'〔International Tables for Crystallography (2006). Volume A, Space-group symmetry.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crystal structure」の詳細全文を読む スポンサード リンク
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