Pressure-induced disappearance of the in-plane lattice distortion in layered cupric chloride: (C2H5NH3)2CuCl4

Effects of hydrostatic pressure on Raman scattering and electronic absorption spectra have been investigated in layered cupric chloride (C2H5NH3)2CuCl4, consisting of strongly Jahn–Teller (JT) deformed CuCl4 layers. We observed selective deactivation of the Cu–Cl stretching modes at a pressure above ∼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 (Cu3dx2−y2) sites by ∼0.4 eV, and perhaps produces the two-dimensional electronic states analogous to that of the parent compounds for the cupric superconductors.