PRESSURE-INDUCED DISAPPEARANCE OF THE INPLANE LATTICE DISTORTION IN LAYERED CUPRIC CHLORIDE - (C2H5NH3)(2)CUCL4

Effects of hydrostatic pressure on Raman scattering and electronic absorption spectra have been investigated in layered cupric chloride (C2H5NH3)(2)CuCl4, consisting of strongly Jahn-Teller (JT) deformed CuCl4 layers. We observed selective deactivation of the Cu-Cl stretching modes at a pressure above similar to 4 GPa, and interpreted the phenomena in terms of disappearance of the in-plane lattice distortion of the CuCl4 layer. The pressure-induced structural change reduces: the charge-transfer (CT)-type gap from the ligand (Cl3p) to metal (Cu3d(x2-y2)) sites by similar to 0.4 eV, and perhaps produces the two-dimensional electronic states analogous to that of the parent compounds for the cupric superconductors.