RAMAN STUDY OF (NH4)2CUCL4.2H2O-I - DYNAMICS AND STRUCTURE IN LOW-TEMPERATURE PHASE

We report the results of a Raman scattering study of (NH4)2CuCl42H2O at 300, 205 and 100°K, in order to elucidate the dynamics and phase transition in this double salt. A group theoretical calculation of the symmetry vectors, in the high temperature phase (D4h14), is made and the various modes are identified. The deuterated compound (ND4)2CuCl4·2D2O has also been investigated to help in identifying the modes involving motion of the ammonium ions and water molecules. Through a careful analysis of the spectra at 100°K, the space group in the low temperature phase has been established as D2d3. The important consequence of this result is that this leads to parallel spatial ordering of ammonium tetrahedra in this compound in the low temperature phase. © 1979.