Raman scattering study of [N(CD 3 ) 4 ] 2 ZnCl 4 under hydrostatic pressure

Raman spectra were measured for [N(CD 3 ) 4 ] 2 ZnCl 4 over the pressure range 1–2000 bar. The influence of pressure was studied for the ZnCl 4 bending modes and the 24 cm −1 phonon peak. The pressure dependence of these modes was interpreted having regard to the phase transitions predicted by the temperature–pressure diagram. The pressure dependence of all the recorded spectra highlights a critical behaviour at about 500 bar which does not correspond to any phase transition in the diagram. This phenomenon was interpreted by consideration of the modulation characteristics.