Abstract
Polarized single crystal Raman spectra of the langbeinite K2Cd2(SO4)3 were recorded for different polarisations. With a view to understanding the phase transition mechanism, the lattice vibrational spectra (0–300 cm−1), as well as the SO4 symmetric stretching mode v 1 (1,022 cm−1), were recorded at different temperatures. No soft modes were observed. From the study of the temperature variation of the integrated intensity I 0 and band width Γ of the hard mode (1,022 cm−1), both SO4 libration and SO4 order/disorder models were ruled out as possible phase transition models. On the other hand, the model of Speer and Salje (paper I), involving the distortion of the polyhedra around Cd and K ions, explains the observed temperature behaviour of the Raman spectra very well. The consequences of a possible hypothetical high-temperature phase are discussed.
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References
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Devarajan, V., Salje, E. Phase transitions in langbeinites II: Raman spectroscopic investigations of K2Cd2(SO4)3 . Phys Chem Minerals 13, 25–30 (1986). https://doi.org/10.1007/BF00307310
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DOI: https://doi.org/10.1007/BF00307310