International
Tables for Crystallography Volume D Physical properties of crystals Edited by A. Authier © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. D. ch. 3.1, p. 365
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Potassium nitrate has a rather simple phase diagram, reproduced in Fig. 3.1.5.9. Two different structures and space groups were proposed for the ambient temperature phase I: Shinnaka (1962) proposed () with two formula groups per primitive cell (), whereas Tahvonen (1947) proposed () with one formula group per primitive cell. In fact, both are wrong. The correct space group is that of Nimmo & Lucas (1973): () with one formula group per primitive cell. Again, Raman spectroscopy of phonons shows that the Tahvonen structure predicts approximately twice as many spectral lines as can be observed. Balkanski et al. (1969) tried creatively but unsuccessfully to account for their spectra in terms of Tahvonen's space-group symmetry assignment for this crystal; later Scott & Pouligny (1988) showed that all spectra were compatible with the symmetry assigned by Nimmo and Lucas. In this case, in contrast to the perovskites strontium titanate and lanthanum aluminate, the confusion regarding space-group symmetry arose from the large degree of structural disorder found in phase I of KNO3. The structures of phases II and III are unambiguous and are, respectively, aragonite () with and () with Z = 1.
References
Balkanski, M., Teng, M. K. & Nusimovici, M. (1969). Lattice dynamics in KNO3. Phases I, II and III. In Light scattering spectra of solids, edited by G. B. Wright, pp. 731–746. Paris: Flammarion.Google ScholarNimmo, J. K. & Lucas, D. W. (1973). The crystal structures of - and -KNO3 and the phase transformations. Acta Cryst. B32, 1968–1971.Google Scholar
Scott, J. F. & Pouligny, B. (1988). Raman spectroscopic study of submicron KNO3 films. J. Appl. Phys. 64, 1547–1551.Google Scholar
Shinnaka, Y. (1962). X-ray study on the disordered structure above the ferroelectric Curie point in KNO3. J. Phys. Soc. Jpn, 17, 820–828.Google Scholar
Tahvonen, P. E. (1947). X-ray structure of potassium nitrate. Ann. Acad. Sci. Fenn. Ser. A, 44–51.Google Scholar