International
Tables for
Crystallography
Volume B
Reciprocal space
Edited by U. Shmueli

© International Union of Crystallography 2006
International Tables for Crystallography (2006). Vol. B. ch. 4.2, p. 438   | 1 | 2 |

Section 4.2.4.5.3. Short-range correlations

H. Jagodzinskia and F. Freyb

aInstitut für Kristallographie und Mineralogie, Universität, Theresienstrasse 41, D-8000 München 2, Germany, and  bInstitut für Kristallographie und Mineralogie, Universität, Theresienstrasse 41, D-8000 München 2, Germany

4.2.4.5.3. Short-range correlations

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The final terms in equations (4.2.4.90)[link] and (4.2.4.93)[link] concern correlations between the orientations of different molecules. Detailed evaluations need a knowledge of a particular model. Examples are compounds with nitrate groups (Wong et al., 1984[link]; Lefebvre et al., 1984[link]), CBr4 (More et al., 1980[link], 1984[link]), and many others (see Sherwood, 1979[link]). The situation is even more complicated when a modulation wave with respect to the occupation of different molecular orientations is superimposed. A limiting case would be a box-like function describing a pattern of domains. Within one domain all molecules have the same orientation. This situation is common in ferroelectrics where molecules exhibit a permanent dipole moment. The modulation may occur in one or more directions in space. The observed intensity in this type of orientationally disordered crystal is characterized by a system of more or less diffuse satellite reflections. The general scattering theory of a crystal with occupational modulation waves follows the same lines as outlined in Section 4.2.3.1.[link]

References

First citation Lefebvre, J., Fouret, R. & Zeyen, C. (1984). Structure determination of sodium nitrate near the order–disorder phase transition. J. Phys. (Paris), 45, 1317–1327.Google Scholar
 First citation More, M., Lefebvre, J. & Hennion, B. (1984). Quasi-elastic coherent neutron scattering in the disordered phase of CBr4. Experimental evidence of local order and rotational dynamics of molecules. J. Phys. (Paris), 45, 303–307.Google Scholar
 First citation More, M., Lefebvre, J., Hennion, B., Powell, B. M. & Zeyen, C. (1980). Neutron diffuse scattering in the disordered phase of CBr4. I. Experimental. Elastic and quasi-elastic coherent scattering in single crystals. J. Phys. C, 13, 2833–2846.Google Scholar
 First citation Sherwood, J. N. (1979). The plastically crystalline state. New York: John Wiley.Google Scholar
 First citation Wong, S. F., Gillan, B. E. & Lucas, B. W. (1984). Single crystal disorder diffuse X-ray scattering from phase II ammonium nitrate, NH4NO3. Acta Cryst. B40, 342–346.Google Scholar








































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