The frequency and temperature dependence of ac-conductivity and phase shift of polycrystalline inclusion compounds (b-CD)2 KI7 16H2O and (b-CD)2 LiI7 14H2O (b-CD 1⁄4 b-cyclodextrin) has been investigated over the frequency and temperature... more
The frequency and temperature dependence of ac-conductivity and phase shift of polycrystalline inclusion compounds (b-CD)2 KI7 16H2O and (b-CD)2 LiI7 14H2O (b-CD 1⁄4 b-cyclodextrin) has been investigated over the frequency and temperature ranges of 0–100 kHz and 240–420K. A Raman spectroscopic study and calorimetric measurements are also accomplished. The Arrhenius exponential behaviour s 1⁄4 s0 exp EW=2KBT of the ac-conductivity for T4275K is caused by the contribution of the metal cations K, Li. This contribution is facilitated by the water-net via the Grotthuss mechanism. The ac conductivity starts deviating from the exponential behaviour with lower increasing rate, at 347K for b-K and at 353K for b-Li reaching a maximum value at 371.1 and 361.8K, respectively, and then decreases rapidly due to the gradual removal of all the water molecules. The values 371.1 and 361.8K are characterized as semiconductor to metal transition temperatures. The shift of the initial Raman peak at 179 ...
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Abstract The γ-cyclodextrin polymer (γ-CDP) and carboxymethyl-γ-cyclodextrin polymer (CM-γ-CDP) cross-linked both by epichlorohydrin were investigated via dielectric spectroscopy over the frequency range 0.1–100 kHz and the temperature... more
Abstract The γ-cyclodextrin polymer (γ-CDP) and carboxymethyl-γ-cyclodextrin polymer (CM-γ-CDP) cross-linked both by epichlorohydrin were investigated via dielectric spectroscopy over the frequency range 0.1–100 kHz and the temperature ranges 122.0–472.4 K and 123.6–460.3 K, respectively. The γ-CDP reveals a thermally reversible transformation of some normal hydrogen bonds to flip-flop type at Ttrans = 199.1 K, whereas the CM-γ-CDP doesn’t show any transformation of hydrogen bonds. Both systems present in the lnσ vs 1/T plot two linear parts following the Arrhenius equation. In the case of γ-CDP, the first linear part during cooling (a) has activation energy Eα = 0.41 eV and during heating (b) has Eα = 0.42 eV in the range 259.7–310.0 K. The second linear part (c) in the range 316.5–357.1 K has Eα = 0.36 eV. The corresponding values of CM-γ-CDP are Eα = 0.32 eV (a), Eα = 0.33 eV (b) in the range 242.1–295.1 K and Eα = 0.91 eV (c) in the range 307–366.1 K. The linear parts (a) and (b) of both polymers are related to the accumulation of protons in the grain-boundary regions as it is depicted in the Cole-Cole plots. The linear part (c) is related to the proton migration from the grain-boundary region to the electrodes and the dehydration process taking place. The ac-conductivity of CM-γ-CDP is considerably higher than that of γ-CDP as the partial hydrogen replacement of some hydroxyl groups by carboxymethyl moiety, renders numerous protons more flexible to move along the hydrogen-bonded network, contributing to the conductivity. Both systems after the dehydration process, presented a newly-formed hydrogen bonded network due to the reorientation of hydrogen bonded chains at T > 397.0 K for γ-CDP and T > 420.9 K for CM-γ-CDP.
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Abstract The β-cyclodextrin polymer (β-CDP) and the carboxymethyl-β-cyclodextrin polymer (CM-β-CDP) cross-linked by epichlorohydrin were investigated by dielectric spectroscopy over the frequency range 0.1–100 kHz in the temperature... more
Abstract The β-cyclodextrin polymer (β-CDP) and the carboxymethyl-β-cyclodextrin polymer (CM-β-CDP) cross-linked by epichlorohydrin were investigated by dielectric spectroscopy over the frequency range 0.1–100 kHz in the temperature ranges 132.6–464.8 K and 132.9–500.9 K, respectively. The β-CDP reveals a reversible order-disorder transformation of some normal hydrogen bonds to flip-flop type at Ttrans = 220.1 K, whereas the CM-β-CDP doesn't show any transformation of hydrogen bonds. The ac-conductivity plot of β-CDP (lnσ vs 1/T) shows a linear part obeying the Arrhenius equation in the range 289.8–268.8 K with Eα = 0.71 eV during cooling and 0.77 eV during heating. A deformed bell-shaped curve with maximum values at Ttrans = 222.7 K during cooling and 223.8 K during heating in the range 132.6–268.8 K, is due to the hydrogen-bonded transformation. At 328.9
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The frequency and temperature dependence of the real and imaginary parts of the dielectric constant (ɛ′,ɛ″), the phase shift (ϕ) and the ac-conductivity (σ) of the polycrystalline (β-Cyclodextrin)2⋅CsI7⋅13H2O (β-Cs) have been investigated... more
The frequency and temperature dependence of the real and imaginary parts of the dielectric constant (ɛ′,ɛ″), the phase shift (ϕ) and the ac-conductivity (σ) of the polycrystalline (β-Cyclodextrin)2⋅CsI7⋅13H2O (β-Cs) have been investigated over the frequency and temperature ranges of 0–100 kHz and 140–425 K, respectively, in combination with Raman spectroscopy and DSC. The ɛ′(T), ɛ″(T) and ϕ(T) variations at frequency
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ABSTRACT
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The frequency dependence of the real (ɛ′) and imaginary (ɛ″) parts of the dielectric constant of polycrystalline hematite (α-Fe2O3) has been investigated in the frequency range 0–100kHz and the temperature range 190–350K, in order to... more
The frequency dependence of the real (ɛ′) and imaginary (ɛ″) parts of the dielectric constant of polycrystalline hematite (α-Fe2O3) has been investigated in the frequency range 0–100kHz and the temperature range 190–350K, in order to reveal experimentally the electron hopping mechanism that takes place during the Morin transition of spin-flip process. The dielectric behaviour is described well by the Debye-type relaxation (α-dispersion) in the temperature regions T<233K and T>338K. In the intermediate temperature range 233K<T<338K a charge carrier mechanism takes place (electron jump from the O2− ion into one of the magnetic ions Fe3+) which gives rise to the low frequency conductivity and to the Ω-dispersion. The temperature dependence of relaxation time (τ) in the −ln τ vs 103/T plot shows two linear regions. In the first, T<238K, τ increases with increasing T implying a negative activation energy −0.01eV, and in the second region T>318K τ decreases as the temper...
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Résumé/Abstract The ac-conductivity and the phase shift of the polycrystalline complex (α-CD) 2· Cd 0.5-Ι 5· 26H 2 Ο (a-CD= a-Cyclodextrin) have been investigated over the frequency and temperature ranges of 0-100 kHz and 240-425 K. A... more
Résumé/Abstract The ac-conductivity and the phase shift of the polycrystalline complex (α-CD) 2· Cd 0.5-Ι 5· 26H 2 Ο (a-CD= a-Cyclodextrin) have been investigated over the frequency and temperature ranges of 0-100 kHz and 240-425 K. A Raman spectroscopy ...
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The frequency and temperature dependence of ac-conductivity and phase shift of polycrystalline inclusion compounds (β-CD)2·KI7·16H2O and (β-CD)2·LiI7·14H2O (β-CD=β-cyclodextrin) has been investigated over the frequency and temperature... more
The frequency and temperature dependence of ac-conductivity and phase shift of polycrystalline inclusion compounds (β-CD)2·KI7·16H2O and (β-CD)2·LiI7·14H2O (β-CD=β-cyclodextrin) has been investigated over the frequency and temperature ranges of 0–100kHz and 240–420K. A Raman spectroscopic study and calorimetric measurements are also accomplished. The Arrhenius exponential behaviour σ=σ0exp(-EW/2KBT) of the ac-conductivity for T>275K is caused by the contribution of the metal cations
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... Molec. Phys. , 100: 673 [Taylor & Francis Online], [Web of Science ®] View all references, 44.Papaioannou, J and Ghikas, T. 2003. Molec. Phys. , 101: 2601 [Taylor & Francis Online], [Web of Science ®] View all references]. All... more
... Molec. Phys. , 100: 673 [Taylor & Francis Online], [Web of Science ®] View all references, 44.Papaioannou, J and Ghikas, T. 2003. Molec. Phys. , 101: 2601 [Taylor & Francis Online], [Web of Science ®] View all references]. All systems showed ionic conductivity at room ...
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The Raman spectra of the cyclomaltoheptaose (beta-cyclodextrin, beta-CD) polyiodide complexes (beta-CD)(2).NaI(7).12H(2)O, (beta-CD)(2).RbI(7).18H(2)O, (beta-CD)(2).SrI(7).17H(2)O, (beta-CD)(2).BiI(7).17H(2)O and... more
The Raman spectra of the cyclomaltoheptaose (beta-cyclodextrin, beta-CD) polyiodide complexes (beta-CD)(2).NaI(7).12H(2)O, (beta-CD)(2).RbI(7).18H(2)O, (beta-CD)(2).SrI(7).17H(2)O, (beta-CD)(2).BiI(7).17H(2)O and (beta-CD)(2).VI(7).14H(2)O (named beta-M, M stands for the corresponding metal) are investigated in the temperature range of 30-140 degrees C. At room temperature all systems show an initial strong band at 178 cm(-1) that reveals similar intramolecular distances of the disordered I(2) units (approximately 2.72 A). During the heating process beta-Na and beta-Rb display a gradual shift of this band to the final single frequency of 166 cm(-1). In the case of beta-Sr and beta-Bi, the band at 178 cm(-1) is shifted to the final single frequencies of 170 and 172 cm(-1), respectively. These band shifts imply a disorder-order transition of the I(2) units whose I-I distance becomes elongated via a symmetric charge-transfer interaction I(2)&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;--I3(-)--&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;I(2). The different final frequencies correspond to different bond lengthening of the disordered I(2) units during their transformation into well-ordered ones. In the Raman spectra of beta-V, the initial band at 178 cm(-1) is not shifted to a single band but to a double one of frequencies 173 and 165 cm(-1), indicating a disorder-order transition of the I(2) molecules via a non-symmetric charge-transfer interaction I(2)&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;--I3(-)--&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;I(2). The above spectral data show that the ability of I3(-) to donate electron density to the attached I(2) units is determined by the relative position of the different metal ions and their ionic potential q/r. The combination of the present results with those obtained from our previous investigations reveals that cations with an ionic potential that is lower than approximately 1.50 (Cs(+), Rb(+), Na(+), K(+) and Ba(2+)) do not affect the Lewis base character of I3(-). However, when the ionic potential of the cation is greater than approximately 1.50 (Li(+), Sr(2+), Cd(2+), Bi(3+) and V(3+)), the M(n+)...I3(-) interactions become significant. In the case of a face-on position of the metal (Sr(2+), Bi(3+)) relative to I3(-), the charge-transfer interaction is symmetric. On the contrary, when the metal (Li(+), Cd(2+), V(3+)) presents a side-on position relative to I3(-), the charge-transfer interaction is non-symmetric.
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... These spectral data were explained by taking into consideration the metaltriiodide interactions which are determined by the ionic potential q/r of the metals [16] and their position relative to I − 3 . Thus, we have drawn the... more
... These spectral data were explained by taking into consideration the metaltriiodide interactions which are determined by the ionic potential q/r of the metals [16] and their position relative to I − 3 . Thus, we have drawn the following general conclusions: I. When the ionic ...
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The frequency and temperature dependence of the real (ε') and imaginary (ε'') parts of the dielectric constant of polycrystalline complex beta-cyclodextrin-4-t-butylbenzyl alcohol [beta-CD TERB 11.2H2O] and beta-cyclodextrin... more
The frequency and temperature dependence of the real (ε') and imaginary (ε'') parts of the dielectric constant of polycrystalline complex beta-cyclodextrin-4-t-butylbenzyl alcohol [beta-CD TERB 11.2H2O] and beta-cyclodextrin [beta-CD 9.8H2O] and of the corresponding dried forms (beta-CD TERB 3.8H2O and beta-CD 2.4H2O, respectively) has been investigated, in the frequency range 0-100kHz and temperature range 130-350K. The dielectric behaviour is described well