International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.8, pp. 335-337

Section 3.8.6.2. Phase transitions in ammonium nitrate

C. J. Gilmore,a G. Barra and W. Donga*

aDepartment of Chemistry, University of Glasgow, University Avenue, Glasgow, G12 8QQ, UK
Correspondence e-mail:  chris@chem.gla.ac.uk

3.8.6.2. Phase transitions in ammonium nitrate

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Ammonium nitrate exhibits temperature-induced phase transformations. Between 256 and 305 K it crystallizes in the orthorhombic space group Pmmm with a = 5.745, b = 5.438, c = 4.942 Å and Z = 2; from 305 to 357 K it crystallizes in Pbnm with a = 7.14, b = 7.65, c = 5.83 Å with Z = 4; between 357 and 398 K it crystallizes in the tetragonal space group [P\overline 4 {2_1}m] with a = 5.719, c = 4.932 Å, Z = 2, and above 398 K it transforms to the cubic space group [Pm\overline 3 m] with a = 4.40 Å and Z = 1. PXRD data containing 75 powder patterns taken at intervals of 3 K starting at 203 K using a D5000 Siemens diffractometer and Cu Kα radiation with a 2θ range of 10–100° were used (Herrmann & Engel, 1997[link]). Fig. 3.8.11[link](a) shows the data in the 2θ range 17–45°.

[Figure 3.8.11]

Figure 3.8.11 | top | pdf |

Ammonium nitrate phase transitions. (a) The raw powder data measured between 203 and 425 K. Reproduced with permission from Herrmann & Engel (1997[link]). Copyright (1997) John Wiley and Sons. (b) The MMDS plot. The purple line follows the temperature change from 203 to 425 K.

The visualization of these data following cluster analysis is shown in Fig. 3.8.11[link](b) using an MMDS plot on which has been superimposed a line showing the route followed by the temperature increments. The purple line follows the transition from a mixture of forms IV and V at low temperature (red) through form IV (yellow), form II (blue) and finally form I at high temperature (green). This is an elegant and concise representation of the data in a single diagram.

References

Herrmann, M. J. & Engel, W. (1997). Phase transitions and lattice dynamics of ammonium nitrate. Propellants Explos. Pyrotech. 22, 143–147.Google Scholar








































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