The temperature evolution of Cu 2+ ion environment in the solid solutions of ((CH 3 ) 2 NH 2 ) 5 Cd 2 CuCl 11 is studied on the basis of absorption spectroscopy data. For the detailed analysis of experimental data the special program package Crys Tool 1.0 based on quantum-mechanical models, first of all on the model of normalized spherical harmonics (NSH), has been employed. It has been found that similarly to the crystal of ((CH 3 ) 2 NH 2 ) 5 Cd 3 Cl 11 (DMACC) the investigated solid solution contains tetragonally distorted octahedral metal-halogen complexes of two types and the degree of their distortion is changed considerably at the temperatures of phase transitions (PTs). The parameters of crystal field, angular overlap model, as well as the copper-chlorine distances, show continuous changes at T 1 = 176 K that should be related to the second-order transition, whereas the jump-like anomalies of the spectral parameters at T 2 = 115 K (on cooling) are characteristic of the first-order PTs. Introduction of the copper ions into the structure of the host DMACC crystal induces the shifts of these PTs toward low temperatures by 3.5 and 5 K, respectively. The observed structural changes around T 0 = 313 K are connected with a complex co-operative effect involving weakening of the hydrogen bonds and modification of the Jahn-Teller distortion with temperature.
This paper presents the results of investigations of the dielectric and spectral properties of NH 2 (CH 3 ) 2 Al(SO 4 ) 2 × 6 H 2 O crystals doped with chromium. In particular, it is shown that the dopant noticeably changes the temperature of ferroelectric phase transition and corresponding thermal dipole relaxation with a critical slowing-down at T c1 . The Cr 3+ ions were used as a convenient probe for investigations of crystalline structure. On the basis of absorption and luminescence spectroscopy and resonance Raman scattering study it has been shown that the metal-hydrate complexes in the investigated crystals possess the considerably distorted octahedral shape.
On the basis of dilatometric and dielectric investigations of NH(CH3)3CuCl3 · 2H2O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T c 1 = 198 K and T h 1 = 223 K, respectively, in cooling and heating runs. Existence of the characteristic dielectric dispersion was revealed within the high-temperature phase. It corresponds to the single dielectric relaxator below 250 K as well as to co-existence of two relaxators above this temperature. The determined values of the activation energy and relaxation time are characteristic of the co-operative reorientation of the trimethylammonium cation (high-frequency relaxator) whereas the combined reorientation motions of the CuCl 2 · 2H 2 O chains would be responsible for the low-frequency relaxation process. It was found that the above mentioned quasi-Debye type processes are involved into the mechanisms of the protonic conductivity.
The dielectric and spectral properties of [NH(CH 3 ) 3 ]CoCl 3 × 2H 2 O (abbreviately TrMA-CoCl 3 ) crystals were investigated in the temperature region of 293-345 K. The anomalous behaviour of the investigated parameters at T 1 = 327 K was related to early unknown phase transition. The considerable change of the absorption spectra at T 1 is explained by the distorsion and the corresponding change of symmetry of the polyhedron around Co 2+ ion.
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