Electron–Phonon Interaction and Phase Transitions in [C2H5NH3]2CuCl4 Crystals

Optical and spectral investigations confirmed the availability of phase transitions in [C 2 H 5 NH 3 ] 2 CuCl 4 at T 1 = 364 K, T 2 h = 356 K, T 3 = 232 K. It has been found that the empirical Urbach rule is fulfilled in all phases. It is shown, that in the high-temperature phases skeletal vibrations of the C-N-C group interact with phonons, whereas in the low-temperature phases internal vibrations of the metal-halogen complex occur. A ferroelastic domain structure was observed using the polarising microscope in the temperature region 232 to 364 K.