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

Abstract

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 h 2 = 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.

Investigations of High Temperature Phase Transitions in (NH3c2H5)2CuCl4Crystals

“…Following optical and spectral investigations confirmed availability of the phase transitions in EA-CuCl 4 at T1 = 364 K, TI = 356 K, T4 = 232 K [3,4], although it was supposed that anomalous behaviour of investigated spectral properties observed both at heating and cooling around the temperature of T = 330 K should be related to earlier unknown phase transition [4]. Such an ambiguity demands further study of the high temperature phase transitions using more precise methods.…”

Dielectric Relaxation in High Temperature Phases of (NH3C2H5)2CuCl4 Crystals

“…The IR absorption bands at room tem- perature were identified in a previous paper [17]. Nevertheless, some additional information would be obtained from the analysis of their temperature evolution (Fig.…”

Temperature Evolution of the Optical Absorption Edge in (NH3C2H5)2CuCl4 Crystals

“…Taking into account that the temperature evolution of the absorption bands, which correspond to the internal transitions of Cu 2 ion and lie below 2 eV, has been investigated fairly well [9], it would be convenient to analyse the behaviour of the absorption edge observed within the energy region 2.5 to 4 eV depending on the polarization of light. One can suggest that the most intensive low energy CT band I in EA-CuCl 4 should be observed when the light is polarized along the directions of the shortest bonds ªligand±metalº in the equatorial plane, namely along [110] and [1 " 10].…”

“…it was suggested that the absorption bands observed within the framework of 1.5 to 2.0 eV are characteristic of the distorted octahedral coordination of the copper ion [9].…”

“…[8]. The strength of EPI was found to be comparatively low s 0 varies its value from 0.424 till 1.800 depending on the crystal phase) and observed broadening of the CT band was very weak.…”