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Raman intensities of the lattice modes of KH1−xDxF2as the order parameter for phase transition

Authors
Journal
Spectrochimica Acta Part A Molecular Spectroscopy
0584-8539
Publisher
Elsevier
Publication Date
Volume
44
Issue
12
Identifiers
DOI: 10.1016/0584-8539(88)80198-3

Abstract

Abstract In this work, the Raman intensities of the librational mode of the bifluoride ion and the translational mode of the K + ion are considered as the order parameters for the phase transition of KH 1−xD xF 2 since group theoretical consideration shows that the Raman active translational and librational modes in the low temperature phase will be inactive in the high temperature phase if the latter is of symmetry group O or higher. The measured Raman intensities are correlated with the temperature from 163°C to 196°C to elucidate the exponent β which relates the Raman intensity to the temperature close to T c through (T c-T) β for various deuteration compositions. The β value of KHF 2 is very close to that predicted by the Ising model of three-dimensional space with a one-dimensional order parameter, suggesting that the nearest-neighbour interaction of the translational modes can play a very important role for the phase transition. Experiments also show that the phase transition temperature is slightly isotope composition dependent.

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