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Interstitials are a variety of crystallographic defects, i.e. atoms which occupy a site in the crystal structure at which there is usually not an atom, or two or more atoms sharing one or more lattice sites such that the number of atoms is larger than the number of lattice sites. They are generally high energy configurations. 〔P. Ehrhart, ''Properties and interactions of atomic defects in metals and alloys'', edited by H. Ullmaier, Landolt-Börnstein, New Series III vol. 25 ch. 2 p. 88- (Springer, Berlin, 1991)〕 Small atoms in some crystals can occupy interstitial sites in an energetically favourable configuration, such as hydrogen in palladium. Interstitials can be produced for instance by particle irradiation above the threshold displacement energy, but may also exist in small concentrations in thermodynamic equilibrium. == Self-interstitials == Self-interstitial defects are interstitial defects which contain only atoms which are the same as those already present in the lattice. The structure of interstitial defects has been experimentally determined in some metals and semiconductors. Contrary to what one might intuitively expect, most self-interstitials in metals with a known structure have a 'split' structure, in which two atoms share the same lattice site. 〔〔Self-interstitial atoms in metals, Journal of Nuclear Materials 69&70 (1978) p. 465.〕 Typically the center of mass of the two atoms is at the lattice site, and they are displaced symmetrically from it along one of the principal lattice directions. For instance, in several common FCC metals such as copper, nickel and platinum, the ground state structure of the self-interstitial is the split () interstitial structure, where two atoms are displaced in a positive and negative () direction from the lattice site. In BCC iron the ground state interstitial structure is similarly a () split interstitial. These split interstitials are often called dumbbell interstitials, because plotting the two atoms forming the interstitial with two large spheres and a thick line joining them makes the structure resemble a dumbbell weight-lifting device. In other BCC metals than iron, the ground state structure is believed based on recent Density-functional theory calculations to be the () crowdion interstitial, which can be understood as a long chain (typically some 10-20) of atoms along the () lattice direction, compressed compared to the perfect lattice such that the chain contains one extra atom. In semiconductors the situation is more complex, since defects may be charged and different charge states may have different structures. For instance, in silicon, the interstitial may either have a split () structure or a tetrahedral truly interstitial one. 〔G. D. Watkins, Native defects and their interactions with impurities in silicon, in Defects and Diffusion in Silicon Processing, edited by T. Diaz de la Rubia, S. Coffa, P. A. Stolk and C. S. Rafferty, MRS Symposium Proceedings vol. 469 p. 139 (Materials Research Society, Pittsburg 1991) 〕 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「Interstitial defect」の詳細全文を読む スポンサード リンク
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