Laser Raman study of the low-temperature phase transformation in [N(CH3)4]2CuCl4 single crystals

Abstract

Abstract The results of a detailed temperature-dependent Raman study of single crystals of [N(CH 3 ) 4 ] 2 CuCl 4 are reported in different spectral regions. The observed splittings of the symmetric stretching modes of the N(CH 3 ) + 4 ion below 250 K and the CuCl 2− 4 ion below 50 K into doublets have been explained as being due to the presence of ions on two energetically inequivalent positions within the lattice. From a temperature dependence of the half-widths, frequency separation, relative intensities of the two components of the CN stretch and other thermosensitive spectral changes, we have discovered a new first order type phase transition in this system at ∼50 K due to ordering of ions from one configuration to another. The reordering in phase IV up to 50 K takes place via continuous movement of cations from the disordered to ordered configuration, but below 50 K the ions freeze in the two inequivalent configurations. The dynamics of ordering of the ions at different temperatures is discussed in this communication.