Paracrystal

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A paracrystal is a model for a semicrystalline substance, which has a certain short-range order in the range of 4.5 to 6  Å , but in contrast to a crystal only has a long-range order determined by so-called coordination statistics .

A paracrystal can, for example, be a crystal close to its melting point at which the periodic order of its atomic groups is in dissolution due to heating. The arrangement of these atom groups does not change suddenly. Another example are polymers with semi-crystalline and amorphous (structureless) areas. Paracrystal theory fills the wide gap between crystalline and amorphous materials, since it contains both states as degenerate borderline cases.

The diffraction of X-rays, neutrons and electron beams on such substances is described quantitatively by the theories of the ideal and real paracrystal.

“The electron density distribution in any substance always corresponds to that of a paracrystal if one can assign an ideal point to each building block of this substance in such a way that the distance statistics of these ideal points from any reference ideal point is the same and the electron configuration of each building block around its ideal point is statistically independent of that of the neighboring building blocks he follows. A building block then corresponds to the material content of a cell of this 'shaky' space lattice, which can itself be addressed as a paracrystal. "

- Rolf Hosemann : The ideal paracrystal… In: Zeitschrift für Physik. 1950.

Quantitative differences in diffraction experiment analyzes based on the theories of the ideal and real paracrystals are often negligible in practice.

Ideal paracrystals, just like ideal crystals, are theoretically infinitely extended in all three spatial directions. According to the empirical α * law, real paracrystals can only reach finite sizes that are indirectly proportional to the components of the tensor of the paracrystalline perturbation. Larger solid aggregates are then composed of micro-paracrystals.

The words "Parakristall", "Paracystallinity" and "Paracrystal" go back to Friedrich Rinne and the years 1932 and 1933.

literature

  • R. Hosemann: Paracrystalline phases. Part I: Origin, labeling and properties . In: Chemical Engineer Technology . tape 42 , no. October 20 , 1970, p. 1252-1258 , doi : 10.1002 / cite.330422004 .
  • R. Hosemann: Paracrystalline phases. Part II: Examples of use and practical significance . In: Chemical Engineer Technology . tape 42 , no. November 21 , 1970, p. 1325-1332 , doi : 10.1002 / cite.330422107 .
  • Rolf Hosemann: Microparacrystals in Physics . In: Physics Journal . tape 34 , no. November 11 , 1978, pp. 511-521 , doi : 10.1002 / phbl.19780341103 .
  • R. Hosemann, A. Fischer, M. Ralek: Microparacrystals and Technology . In: Physics Journal . tape 36 , no. November 11 , 1980, pp. 334–336 , doi : 10.1002 / phbl.19800361104 .

Web links

Individual evidence

  1. ↑ M. Popescu, H. Bradaczek: Microparacrystalline model for medium-range order in non-crystalline chalcogenides . In: Journal of Optoelectronics and Advanced Materials . tape 3 , no. 2 , June 2001, p. 249–254 ( dtic.mil [PDF; 437 kB ; accessed on September 21, 2016]).
  2. ↑ R. Hosemann: Fundamentals of the theory of the paracrystals and their possible applications in the investigation of the real structure of crystalline substances . In: Crystal and Technology . tape 11 , 1976, p. 1139-1151 .
  3. ^ R. Hosemann: X-ray interference on line grids with fluid disorder . In: Journal of Physics . tape 127 , no. 1-2 , 1950, pp. 16-40 , doi : 10.1007 / BF01338981 .
  4. ↑ R. Hosemann: X-ray interference on substances with liquid-statistical lattice disturbances . In: Journal of Physics . tape 128 , no. 1 , 1950, p. 1-35 , doi : 10.1007 / BF01339555 .
  5. ^ R. Hosemann, SN Bagchi: Direct analysis of diffraction by matter . North Holland Pub. Co .; Interscience Publishers, Amsterdam; New York 1962, OCLC 1862561 .
  6. ↑ R. Hosemann: The ideal paracrystal and the coherent X-ray radiation scattered by it . In: Journal of Physics . tape 128 , no. 4 , 1950, p. 465-492 , doi : 10.1007 / BF01330029 .
  7. ^ R. Hosemann, W. Vogel, D. Weick, FJ Baltá-Calleja: Novel aspects of the real paracrystal . In: Acta Crystallographica Section A . tape 37 , no. 1 , January 1981, pp. 85-91 , doi : 10.1107 / S0567739481000156 .
  8. ^ R. Hosemann, MP Hentschel, FJ Balta-Calleja, E. Lopez Cabarcos, AM Hindeleh: The α * -constant, equilibrium state and bearing netplanes in polymers, biopolymers and catalysts . In: Journal of Physics. C: Solid State Physics . tape 18 , no. 5 , June 2001, p. 249-254 ( iop.org ).
  9. ↑ AM Hindeleh and R. Hosemann: Microparacrystals: The intermediate stage between crystalline and amorphous . In: J. Materials Sci . tape 26 , 1991, pp. 5127-5133 , doi : 10.1007 / BF01143202 .
  10. ↑ F. Rinne: About relationships of the watered bromophenanthrene sulfonic acid to organismic paracrystals . In: Journal of Crystallography. Crystalline Materials . tape 82 , 1932, doi : 10.1524 / zkri.1932.82.1.379 .
  11. ^ Friedrich Rinne: Investigations and considerations concerning paracrystallinity . In: Transactions of the Faraday Society . tape 29 , no. 140 , January 1933, ISSN  0014-7672 , p. 1016-1032 , doi : 10.1039 / TF9332901016 .