Abstract
The Raman spectra of mixed crystals of [(NH4)1−x K x ]2 SO4 in the region 50–3400 cm−1 at 293 K and below 223 K have been reported. At room temperature 293 K, as the concentration of K+ ion increases in the crystal up to 50%, the frequencies of the totally symmetric vibrations of SO 2−4 and NH +4 ions increase and thereafter the frequency of SO 2−4 vibration decreases and attains the value in K2SO4. This change in frequency up to 50% of potassium concentration is due to the breaking of hydrogen bonds of the type N-H...O. The behaviour of Raman intensities of A g (v 1) mode of SO 2−4 for various concentrations (x=0, 0·03, 0·11, 0·5, 0·85) suggest that the phase transition changes from first order type to one of second order. The phase transition in mixed crystals of [(NH4)1−x K x ]2 SO4 can be a cooperative phenomenon arising from a coupling between (NH4)+ ions through hydrogen bonds with the distorted SO 2−4 ions in the low temperature phase.
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Srinivasan, V., Subramanian, C.K. & Narayanan, P.S. Laser Raman spectra of mixed crystals of [(NH4)1−x Kx]2 SO4 . Pramana - J Phys 21, 41–50 (1983). https://doi.org/10.1007/BF02846830
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DOI: https://doi.org/10.1007/BF02846830