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Intramolecular and Lattice Dynamics in V_{6-n}^{IV}V_ n^V O_7(OCH_3)_{12} Crystal

100%
Yablokov Y., Augustyniak-Jabłokow M., Borshch S., Daniel C., Hartl H.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
271-281
EN
Multi-nuclear mixed-valence clusters V_4^{IV}V_2^VO_7(OCH_3)_{12} were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four V^{IV} ions with individual spin S_i=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150 cm^{-1} and the double jump one resulting in dynamics. The dependence of the transition ratesν_{tr} on the energy of the total spin states was observed. In particular, in the range 300-220 K theν_{tr} ≈0.7×10^{10} cm^{-1} and below 180 K the ν_{tr}≈1×10^{10} cm^{-1} was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial V^{IV} ions localization was discovered.
2
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The Origin of EPR Signals in SrCuO_2 Ceramics

100%
Augustyniak-Jabłokow M., Yablokov Y., Ivanova T., Jacyna-Onyszkiewicz I., Shustov V.
Acta Physica Polonica A
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2005
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vol. 108
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issue 2
345-351
EN
The origin and thermal evolution of the EPR signals in SrCuO_2 ceramics are studied. It has been shown that the EPR signals observed in this ceramic material are due to contamination with other phases. The axial signal is due to SrCu(OH)_4·H_2O, which is a product of water reactions with SrCuO_2.
3
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EPR Study of Water Induced Decomposition of the SrCuO_2 and Sr_2CuO_3 Ceramics Surface. The Role of Carbon Dioxide

100%
Augustyniak-Jabłokow M., Yablokov Y., Jacyna-Onyszkiewicz I., Ivanova T., Shustov V.
Acta Physica Polonica A
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2007
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vol. 112
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issue 3
525-536
EN
Processes of SrCuO_2 and Sr_2CuO_3 ceramics decomposition induced by contact with water and carbon dioxide were studied by EPR. The dominant signals in the spectra were found to originate from Sr_2Cu(OH)_6 (for Sr_2CuO_3) and SrCu(OH)_4·H_2O (for SrCuO_2) compounds. The thermally induced conversion of SrCu(OH)_4·H_2O into Sr_2Cu(OH)_6 was analysed, and its product CuO was found to exist in the nanocrystalline form. The presence of CO_2, reacting with Sr(OH)_2, was shown to modify the decomposition process leading to the appearance of SrCu(OH)_4·H_2O, some hydroxycarbonates and Cu(OH)_2 on the surface of ceramics studied. At temperatures higher than 300ºC CuO reacts back with Sr(OH)_2. For the samples being in contact with atmospheric moisture this compound, deposited on a surface of SrCuO_2, decomposes to Sr_2Cu(OH)_6. The presence of the antiferromagnetic compounds Cu(OH)_2, CuO, and Cu_2[(OH)_2CO_3] in the samples can influence the results of magnetic measurements of the studied ceramics.
4
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EPR Discovery of a New Pressure-Induced Low-Spin Phase in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)_2]

86%
Krupska A., Augustyniak-Jabłokow M., Yablokov Y., Zelentsov V., Ulanov V., Mroziński J.
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EN
Electron paramagnetic resonance studies of the high-spin (HS) ↔ low-spin (LS) transition in 2-methyl-5-ethyl-pyridine-5-chloro-salicylalt hiosemicarbazonatoferrate(III) performed under hydrostatic pressure up to 500 MPa in a temperature range of 80-310 K have revealed two modifications of the low spin complexes: low-pressure (LS1) and high-pressure (LS2) ones. Under atmospheric pressure LS1 appears on cooling and disappears on heating at 220 K. The hydrostatic pressure shifts the transition to higher temperatures. Below 275 K an increase in pressure to 410 MPa results in abrupt changes in the g-factor and widthΔ B of the EPR line indicating a transition to a new phase. The pressure-induced transition LS1 ↔ LS2 is almost independent of T up to 275 K, where at a pressure of 420 MPa a triple point is observed. The LS1↔ LS2 and HS↔ LS2 (at T>260 K) transitions occur with a large hysteresis of about 95 MPa. The process of the spin transition has been shown to begin with the formation of domains of LS complexes in the matrix of HS ones. The response of the domains to external factors has been studied.
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