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1
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Effects of Vibronic Dynamics of Cu(H_2O)_6 Complexes and Electron Spin Relaxation in Temperature Dependence of EPR Linewidth in Diamagnetic Tutton Salt Single Crystals

100%
Hoffmann S., Goslar J.
Acta Physica Polonica A
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2006
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vol. 110
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issue 6
807-816
EN
EPR linewidth of Cu^{2+} in the Tutton salt crystals weakly depends on temperature at low temperatures and then it rapidly grows above 60 K. We present detailed results of measurements and analysis for ^{63}Cu^{2+} in K_2Zn(SO_4)_2·6 H_2O, K_2 Zn(SO_4)_2·6D_2O, (NH_4)_2Mg(SO_4)_2·6H_2O and Cs_2Zn (SO_4)_2·6H_2O in a temperature range of 4.2-300 K and compare them with already published electron spin-lattice relaxation data. The relaxation contributes weakly to the linewidth which is dominated by molecular dynamics and grows exponentially with temperature. To describe this we are discussing the influence of jumps between two sites of Cu^{2+} complexes in a slow motion region where the sites are differently thermally populated. This case has not been considered so far. We have derived appropriate expressions describing the contribution of jumps to the linewidth which allows the determination of the jump rate and energy difference δ_{A,B} between the two sites being two Jahn-Teller distorted configurations of the vibronic Cu(H_2O)_6 complexes. The jump rate 1/τ strongly depends on temperature and reaches 10^9 s^{-1} at room temperature, whereas theδ_{A,B} varies from 117 cm^{-1} for K_2Zn(SO_4)_2·6D_2O to 422 cm^{-1} for Cs_2Zn(SO_4)_2·6 H_2O. The comparison with vibronic level splitting, which varies in the range of 67-102 cm^{-1}, indicates that the reorientation mechanism involves phonon induced tunnelling via excited vibronic levels. These reorientations do not contribute, however, to the spin-lattice relaxation which is governed by ordinary two-phonon relaxation processes in the whole temperature range. Thus, the reorientations and spin relaxation are two independent phenomena contributing to the total linewidth.
2
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ESR and Electron Spin Echo Studies of Spin-Lattice Relaxation of Hydrazinium Radical in Li(N_{2}H_{5})O_{4} Single Crystal

81%
Morawski P., Hoffmann S. K., Hilczer W., Goslar J.
Acta Physica Polonica A
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1997
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vol. 91
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issue 6
1121-1129
EN
A hydrazinium ṄH-NH_{3}^{+} radical was identified by ESR in γ-irradiated Li(N_{2}H_{5})SO_{4} single crystal. Unpaired electron is strongly localized on the nitrogen atom as compared to hydrazinium radicals in other crystals. Angular variations of the multicomponent ESR spectra and computer calculations gave the isotropic hyperfine coupling parameters (in mT): a_{N1} = 1.93, a_{N2} = 0.80, a_{H1} = 2.50, a_{H1'} = 0.48 (NH_{3}), and a_{H2} = 1.40 (adjacent molecule). The radiation defects containing unpaired electrons do not influence much the protonic conductivity along the hydrazine molecule chains in the crystal. It confirms a tunelling mechanism of the conductivity activated by NH_{2}-group rotation. Spin-lattice relaxation time T_{1} varies strongly with temperature in the range from 100 ms (10 K) to 90 μs (170 K) and is governed by spectral diffusion (1/T_{1} ∝ T^{2}) and a Murphy-type mechanism (1/T_{1} ∝ cosech(Δ/T)) with Δ = 150 cm^{-1}. A distribution of the spin-relaxation times was observed with temperature independent dispersion parameter β = 0.76.
3
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Applications of the Transport Integrals in Solid-State Physics and in Electron Spin Relaxation

81%
Radczyk T., Hoffmann S., Goslar J.
Acta Physica Polonica A
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2003
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vol. 104
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issue 5
469-477
EN
Transport integrals I_n(Θ_D/T) are reviewed with their applications in solid-state physics, molecular dynamics, and electron spin-lattice relaxation. Analytical approximations of I_n for n=2-8 are proposed as applicable for computer fitting procedures in the range of the variable x=Θ_D/T from 0.1 to 40. The results are applied for description of the spin-lattice relaxation data collected for Cu^{2+} ions in triglycine sulphate and are compared with relaxation data for Cu^{2+} and Mn^{2+} in (NH_4)_2Mg(SO_4)_2·6H_2O.
4
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The Role of Ferric(III) Oxide in Poly-(1,4-Phenylene Sulphide) Curing. EPR and X-ray Studies

81%
Wejchan-Judek M., Hoffmann S., Goslar J., Garbarczyk J.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
107-112
EN
Commercially available poly-(1,4-phenylene sulfide) = PPS with trade names TEDUR and RYTON contain a great amount of Fe(III) (order of 10^{20} Fe/gram) as shown by electron spin resonance spectra. The curing of the pure and Fe-doped (0.2% Fe_2O_3) PPS polymers proves that Fe(III) can be used for improvement of the PPS strength by increasing the polymer cross-linking and a decrease in the polymer crystallinity degree as shown by X-ray diffraction.
5
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Electron Spin Relaxation of Cu(II) Ions in ZnGeF_6·6H_2O Crystal with Strong Jahn-Teller Effect

81%
Idziak S., Hoffmann S., Goslar J.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
177-185
EN
Cu^{2+} ions doped to ZnGeF_6·6H_2O substitute the host Zn^{2+} ions and undergo a strong Jahn-Teller effect producing nearly axial elongation of the Cu(H_2O)_6 octahedra with equal population of the three possible deformations at low temperatures as shown by the EPR spectra. Reorientations between these distorted configurations are observed as a continuous shift of EPR lines leading to averaging of the g- and A-tensors. The full averaging is observed at the phase transition temperature 200 K. Electron spin relaxation was measured up to 45 K only, where the electron spin echo signal was detectable. Electron spin-lattice relaxation is governed by the Raman two-phonon process allowing to determine the Debye temperature asΘ_D=99 K. There is no contribution of the Jahn-Teller dynamics to the spin-lattice relaxation rate. Electron spin echo decay is strongly modulated by dipolar coupling to the ^1H and ^{19}F nuclei. The phase memory time is governed by instantaneous diffusion at helium temperatures and then by spin-lattice relaxation processes and excitation to the first vibronic level of energyΔ=151 cm^{-1}.
6
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Binding of the Trace Elements: Cu(II) and Fe(III) to the Native and Modified Nutritive Potato Starches Studied by EPR

81%
Śmigielska H., Lewandowicz G., Goslar J., Hoffmann S.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
303-310
EN
The Cu(II) and Fe(III) ions have been adsorbed by four potato starches of different degrees of oxidation (different numbers of COOH groups replacing host CH_2OH groups): native (no oxidized), white (pudding) with oxidation degree of 0.04%, gelating (0.1%), and LUBOX starch (0.5%). Concentration of the ions in starches was determined from atomic absorption and EPR spectrum intensity. For small concentration of the adsorbed ions (below 4 mg/g) nearly all ions are adsorbed from the solution. EPR shows that adsorbed copper(II) ions are chemically bonded to the starch molecules (preferably) at COOH sites and uniformly dispersed in the starch structure. The complexes are typical of octahedral or square-quadratic coordination with spin-Hamiltonian parameters g_ǁ=2.373, g_⊥= 2.080, A_ǁ=12.1 mT, A_⊥=1.0 mT. For higher concentrations the Cu(II) displays a tendency to clustering. Iron(III) ions are introduced into starch in a form of clusters mainly, even for the smallest concentration. The highest concentrations of both Cu(II) and Fe(III) were observed in LUBOX starch having the highest degree of oxidation.
7
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Studies of Fast Electron Irradiated Ferroelectric Poly(Vinylidene Fluoride)

81%
Goslar J., Hilczer B., Smogór H.
Acta Physica Polonica A
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2005
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vol. 108
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issue 1
89-94
EN
Radiation-induced functionalization of ferroelectric poly(vinylidene fluoride) was studied by ESR spectroscopy. The samples were irradiated in the high vacuum of a Van de Graaff accelerator with 1.0 MeV and 1.5 MeV electrons at room temperature and the decay of free radicals was studied after transferring the samples into the air. The samples exhibit a multicomponent ESR spectrum that can be decomposed into: a large asymmetric signal in the centre related to peroxy radicals, a quintet with hyperfine splitting A_F = 4.3 mT centred at g = 2.004, assigned to the in-chain radical (-CF_2-CH-CF_2-), and a triplet due to an end-chain (-CH_2) radical with A_H = 1.6 mT and g = 2.009.
8
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Electron Spin Echo Envelope Modulation Analysis of SeO¯_{3} Radical in (NH_{4})_{3}H(SeO_{4})_{2} Single Crystal

71%
Tritt-Goc J., Goslar J., Hilczer W., Hoffmann S., Augustyniak M.
Acta Physica Polonica A
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1993
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vol. 84
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issue 6
1131-1141
EN
A detailed computer analysis of the electron spin echo envelope modulations of SeO_{3} radical in a suitable orientation of (NH_{4})_{3}H(SeO_{4})_{2} single crystal is presented. It was found that the modulations are due to a weak dipolar coupling with nitrogens and protons of the only two neighbouring NH_{4} groups among the five NH_{4} groups surrounding SeO¯_{3} center. Isotropic dipolar coupling constant is 1.7 MHz for nitrogens and 0.9 MHz for protons. It was shown that thermal reorientations of NH_{4} groups observed by NMR have a negligible effect on the electron spin echo envelope modulation pattern but can be responsible for the same value of a^{H}_{iso} for all protons in a NH_{4} group. A good fit obtained between experimental spectra and theoretical calculations assuming nondisturbed crystal geometry indicates a small damage of the crystal by X-rays during the radical center formation.
9
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Structure Characterization and Catalytic Properties of Cr_2O_3 Doped with MgO Supported on MgF_2

71%
Goslar J., Wojciechowska M., Zieliński M., Tomska-Foralewska I., Przystajko W.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
323-330
EN
A characterization of double oxide systems containing Cr_2O_3 doped with MgO and supported on MgF_2 was carried out. The catalysts were prepared by impregnation and co-impregnation methods and characterized by the Brunauer-Emmett-Teller method, EPR, and temperature programmed reduction. The results proved the interactions between supported oxides and the presence of spinel-like phase after treatment at 400ºC. Magnesium oxide clearly influences the catalytic activity as well as selectivity of chromium catalysts supported on MgF_2. The MgO-Cr_2O_3/MgF_2 systems were active and selective in the reaction of CO oxidation at the room temperature and in the dehydrogenation of cyclohexene.
10
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EPR and Spectral Studies of a Molecular and Crystal Structure of Cu (3,5-dimethylpyridine)_{3}(NO_{3})_{2}

71%
Hoffmann S., Goher M., Hilczer W., Goslar J., Hafez A.
Acta Physica Polonica A
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1994
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vol. 85
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issue 3
517-530
EN
X-band single crystal EPR, IR and UV-VIS data are used to deduce a molecular and crystal structure of a new compound with a chemical formula Cu(3,5-dimethylpyridine)_{3}(NO_{3})_{2}. EPR shows that four magnetically inequivalent molecules exist in the crystal unit cell of C_{4v} symmetry. IR spectra suggested that both monodentate and bidentate NO_{3}-groups exist in the crystal. A most probable Cu(II) complex geometry with d_{x²-y²} ground state is a square pyramid with three nitrogens from 3,5-dimethylpyridine molecules and one oxygen from monodentate nitrato group in a basal plane and an oxygen from NO_{3}-group in apical position. There exists a chemical contact between complexes as it is indicated by the exchange interaction with |J| ≤ 1 cm^{-1}. It suggests that square pyramid complexes are arranged in polymeric chains with semi-coordination of bidentate NO_{3}-group to the adjacent Cu(II) ion. An extended analysis of an exchange averaging effect between EPR lines from two and four Cu(II) sites is presented with equations relating molecular and crystal g-factors.
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