Raman spectra in solid solutions of rochelle salt-ammonium rochelle salt

The Raman spectra of NaK1-x(NH4)xC4O·4H2O (RS-ARS) with x = 0; 0.25; 0.87; 0.92; 1.00 Which do not, in practice, differ over the range 200< v <3500 cm-1 excluding the appearance of new lines corresponding to NH4+-oscillations when x increases are investigated. From the other hand, the low-frequency spectra transform considerably. The most essential reconstructions occur in the range 10-200 cm-1 and in particular, in x(zy) z-orientation corresponding to 3-symmetry phonons there appears the relaxation-type wing in the range v < 50 cm-1.This relaxation mode is considered as the second order parameter which is necessary for describing the physical properties of RS-ARS crystals besides the order parameter describing the improper P21212-P1211 phase transition in the crystals with 0.9 × 1.0. Using this two-parameter approximation the phenomenological description of the phase transitions in ammonium-riched RS-ARS is proposed. The phase phenomenological diagram in which the possible thermodynamical paths are shown...