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

Abstract

On the basis of dilatometric, optical, and dielectric investigations of (NH3C2H5)2CuC14 crystals the existence of phase transitions at T1 = 364 and T2 = 356 K was confirmed. Anomalous behaviour of the thermal expansion coefficient and optical birefringence around T3 = 330 K was related to earlier unknown phase transition. Besides, it was shown that these crystals are characterised by considerable protonic conductivity, the nature of which is fairly well explained in the framework of Grotthus mechanism of proton transport.

Electronic spectra of [(CH3)2NH2]5Cd2CuCl11 crystals

“…Under such circumstances the tetragonality factor T should be temperature dependent at T ≥ T 0 similarly to the case of some other Cu-containing crystalline compounds [8]. Assuming, by analogy with [9], that Cu 2+ ions are randomly distributed among the metallic sites of the metal-chorine layer lying in the (ab) plane, it is necessary to take into account the cooperative nature of the Jahn-Teller effect. This is connected with interaction between the neighbouring copper-chlorine octahedra within the complex [Cd 3-x Cu x Cl 11 ] 5-unit (where, as a matter of fact, x would randomly vary from 0 to 3).…”

“…Analysis of the obtained absorption spectra was performed using computer deconvolution of the complex absorption bands into the elementary Gaussian lineshapes corresponding to the actual electron transitions [5,9]. The crystal field theory, and more contemporary models [6 -8, 10, 11] developed on its basis, are known to be useful for unambiguous assignment of the observed bands and the further analysis of the crystal-structure transformations.…”

Dielectric and Dilatometric Properties of NH(CH3)3CuCl3·2H2O Low Dimensional Ferroics

“…On the basis of the available structural [1] and dielectric data for related materials [13,14,20,21] one can suppose that in the case of the high-frequency relaxator the determined values of the relaxation time are characteristic of the co-operative reorientation of the trimethylammonium groups between neighbour copper-chlorine chains along [011]. The values of the relaxation time for the lowfrequency relaxator are considerably larger.…”

“…It is clearly seen that the conductivity depends exponentially on temperature that is characteristic of hopping conductivity. This type of conductivity is described by equation [20]:…”

“…Cl bonds between neighbor copper-chlorine chains along [011] (high-frequency relaxator). One can suggest that the co-operative reorientation of the organic groups proceeds along [011] whereas the translocation of protons between the neighboringchains of CuCl 2 · 2H 2 O is observed in the perpendicular direction, that is along [011] [20]. In this case, to permit a proton transport, the activation energy of conductivity E a has to be larger than the sum of the activation energy E r of the host molecule reorientation and the energy barrier U between the two different H-bonds.…”