Substitution solid solution

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As a substitution mixed crystal , or substitutional solid solution , a is a mixed crystal referred to in which at least two substances a common crystal form and the atoms of the second component on the regular lattice sites sitting of the first component.

Examples of exchange solid solutions
Exchange solid solution, face-centered cubic
Exchange solid solution, space-centered cubic
black = atoms of element 'A'

red = atoms of element 'B'

The prerequisites for this are:

  1. atoms of approximately the same size (difference max. 15%)
  2. same lattice configuration (the crystal types A and B must be the same)
  3. chemical affinity of the components (approximately the same number of valence electrons in both components; the metals must be adjacent in the periodic table, electronegativities must be similar)

The distribution of the foreign atoms in the crystal can be completely unregulated (i.e. statistically distributed). A substitution solid solution with a statistical arrangement does not represent a stoichiometric connection of the individual components. In contrast, superstructures (or long-range order) are a special case of substitution solid solutions, which occur with certain integer mixing ratios of the components (example: CuAu, Cu 3 Au). In these, the foreign atoms are in an orderly distribution. There is also a short-range order in which the host atoms form larger, coherent areas, whereas the foreign atoms are less often directly next to each other. A fourth possibility is that the dissolved foreign atoms are present in certain areas in greater concentration, in so-called zones.

For the lattice constant of the mixed crystal, Vegard's rule applies approximately , according to which it results from the arithmetic mean of the lattice constants of the components.

Special cases for substitution solid solution

  • Local arrangement: No completely random arrangement of B atoms in the A lattice.
  • Superstructure: regular arrangement of B atoms in the A lattice; stoichiometric AB ratio.
  • Single-phase segregation (cluster formation) or coherent segregation: Local accumulation of B atoms in the A lattice is of particular importance in precipitation- hardened materials (e.g. AlCuMg , AlMgSi )

Examples

literature

  • Charles Kittel: Introduction to Solid State Physics. Oldenbourg, 11th edition 1996, ISBN 3-486-23596-6 .

See also

Individual evidence

  1. ^ Rainer Schwab: Materials science and material testing for dummies . John Wiley & Sons, 2011, ISBN 978-3-527-70636-5 , pp. 94 ( limited preview in Google Book search).
  2. ↑ Frank Hahn: Practical course in materials technology: Testing and understanding materials . Carl Hanser Verlag GmbH Co KG, 2015, ISBN 978-3-446-44494-2 , pp. 18 ( limited preview in Google Book search).
  3. ↑ a b c d e f Tarsilla Gerthsen: Chemistry for mechanical engineering . KIT Scientific Publishing, 2006, ISBN 978-3-86644-079-1 , pp. 255 ( limited preview in Google Book search).
  4. ↑ Bernhard Ilschner: Material science properties, processes, technologies . Springer-Verlag, 2013, ISBN 978-3-662-10911-3 , pp. 49 ( limited preview in Google Book search).
  5. ↑ Wolfgang Bergmann: Material engineering 1 Structural structure of materials - Metallic materials - Polymer materials - Non-metallic-inorganic materials . Carl Hanser Verlag GmbH Co KG, 2013, ISBN 978-3-446-43581-0 , p. 61 ( limited preview in Google Book search).