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

On the basis of dielectric investigations of (NH 3 C 2 H 5 ) 2 CuCl 4 crystals the existence of phase transitions at T 1 ¼ 364 K and T 2 ¼ 356 K (in a heating run) was confirmed. In the temperature region of 300-370 K Debye relaxation was observed. The change of the dielectric dispersion character around T 3 ¼ 330 K is related to the phase transition. The determined values of the activation energy and the times of the dielectric relaxation for all phases are characteristic of the combined reorientation motions of the alkylammonium cation. The conclusions concerning the dynamics of the hydrogen bonds were confirmed by IR spectroscopy.Na osnovanii dannyh di+lektriqeskih issledovanij kristallov (NH 3 C 2 H 5 ) 2 CuCl 4 podtverwdeno naliqie fazovyh perehodov pri T 1 ¼ 364 K i T 2 ¼ 356 K (v rewime nagreva). V oblasti temperatur 300-370 K nablˇdalas# debaevska¾ relaksaci¾. Izmenenie haraktera di+lektriqeskoj dispersii v okrestnosti T 3 ¼ 330 K otneseno k fazovomu perehodu. Rassqitannye znaqeni¾ +nergii aktivacii i vremen di+lektriqeskoj relaksacii dl¾ vseh faz ¾vl¾ˇts¾ harakternymi dl¾ kooperativnoj pereorientacii alkilammonievogo kationa. Vyvody o dinamike vodorodnyh sv¾zej podtverwdeny dannymi IK spektroskopii.

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

Korchak

Kapustianik

Tchukvinskyi

et al. 2001

phys. stat. sol. (b)

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Electronic Spectra and Crystal Structure of the Layered Compounds (CnH2n+1NH3)2CuCl4 (n = 2, 3) in the Region of Their Phase Transitions

Kapustianik

Bazhan

Korchak

2002

phys. stat. sol. (b)

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On the basis of absorption spectroscopy data the temperature evolution of Cu 2þ ion environment in the layered compounds (C n H 2nþ1 NH 3 ) 2 CuCl 4 (n ¼ 2, 3) was studied. For the detailed analysis of experimental data the special program package CrysTool 1.0 based on quantum mechanical models using normalized spherical harmonics (NSH) has been created. It has been found that both crystals contain tetragonally distorted octahedral metal-halogen complexes and that the degree of distortion is less pronounced in the low-temperature phases. The phase transitions (PTs) in both compounds were found to be connected with gradual ordering of the organic cations at cooling. For (C 2 H 5 NH 3 ) 2 CuCl 4 the parameters of crystal field, normalized spherical harmonics, and angular overlap model as well as the metal-halogen distances show jump-like anomalies at the points of PTs (T 1 ¼ 364 K and T 2 ¼ 356 K, at heating), whereas a continuous change was observed at T 3 ¼ 330 K.Na osnovanii dannyh absorbcionnoj spektroskopii issledovana temperaturna¾ +volˇci¾ okruweni¾ iona Cu 2þ v sloistyh soedineni¾h (C n H 2nþ1 NH 3 ) 2 CuCl 4 (n ¼ 2, 3). Dl¾ detal#nogo analiza +ksperimental#nyh rezul#tatov sozdan special#nyj programmnyj paket CrysTool 1.0, baziruˇ §ijs¾ na kvantovo-mehaniqeskih model¾h, v pervuǒ qered#, na modeli normirovannyh sferiqeskih garmonik (NSG). Obnaruweno, qto oba kristalla soderwat tetragonal#no deformirovannye okta+driqeskie metal-galogennye kompleksy i stepen# distorsii menee vyrawena v nizkotemperaturnyh fazah. Pokazano, qto fazovye perehody (FP) v obeih soedineni¾h sv¾zany s postepennym upor¾doqeniem organiqeskih kationov pri ohlawdenii. Dl¾ (C 2 H 5 NH 3 ) 2 CuCl 4 parametry kristalliqeskogo pol¾, normirovannyh sferiqeskih garmonik, modeli uglovogo perekryvani¾ tak we, kak i metall-galogennye rassto¾ni¾ preterpevaˇt skaqkoobraznye anomalii v toqkah FP (T 1 ¼ 364 K i T 2 ¼ 356 K, pri nagreve), v to vrem¾ kak nepreryvna¾ anomali¾ obnaruwena pri T 3 ¼ 330 K.

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Exciton–phonon interaction and Raman spectra of [(CH₃)₂NH₂]₅Cd₂CuCl₁₁ crystals

Kapustianik

Batiuk

Czapla

et al. 2004

Physica Status Solidi (b)

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Temperature evolution of the exciton-phonon interaction (EPI) in ((CH 3 ) 2 NH 2 ) 5 Cd 2 CuCl 11 solid solution was studied on the basis of absorption spectroscopy data. The obtained values of effective phonon energies were compared with the data of Raman spectroscopy. It is shown that the σ(T) and E ′ parameters of Urbach's rule show the continuous anomalous change characteristic of the second-order phase transition at T 1 = 176 K. The anomalous behaviour of the EPI and other spectral parameters at T 0 = 310 -315 K was related to the complex co-operative effect involving weakening of the hydrogen bonds and variation of the Jahn-Teller distortion of metal-halogen polyhedra with temperature. This process takes place only within the copper-chlorine sublattice and due to this would be hardly related to the usual phase transition. At the same time, the considered temperature change of the tetragonal distortion of the metal-halogen octahedra is followed by nonfulfillment of Urbach's rule in the temperature range T ≥ T 0 .

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

Cited by 9 publications

References 10 publications

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

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

Electronic Spectra and Crystal Structure of the Layered Compounds (CnH2n+1NH3)2CuCl4 (n = 2, 3) in the Region of Their Phase Transitions

Exciton–phonon interaction and Raman spectra of [(CH₃)₂NH₂]₅Cd₂CuCl₁₁ crystals

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

Cited by 9 publications

References 10 publications

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

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

Electronic Spectra and Crystal Structure of the Layered Compounds (CnH2n+1NH3)2CuCl4 (n = 2, 3) in the Region of Their Phase Transitions

Exciton–phonon interaction and Raman spectra of [(CH3)2NH2]5Cd2CuCl11 crystals

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Exciton–phonon interaction and Raman spectra of [(CH₃)₂NH₂]₅Cd₂CuCl₁₁ crystals