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14 results on '"Wojnarowska, Zaneta"'

4. Effect of Temperature, Pressure and Aging time on the Relaxation Dynamics of Bi0.9Gd0.1Fe0.9Mn0.1O3 System: Direct Evidence of Glassy State and Pressure Induced Relaxor Behavior

Author

Tripathy, Satya N., Wojnarowska, Zaneta, Knapik, Justyna, Chrobak, Arthur, Pradhan, Dillip K., Pawlus, Sebastian, and Paluch, Marian

Subjects
Condensed Matter - Materials Science
Abstract

The fundamental aspects of relaxation dynamics in Bi0.9Gd0.1Fe0.9Mn0.1O3 multiferroic system have been reported. The study was carried out employing dielectric relaxation spectroscopy covering eight decades in frequency 0.01 to106 Hz and in a wide range of temperature 423 K to 153 K, hydrostatic pressure 0.1 MPa to 1765 MPa and aging time 0 s to 80000 s. The temperature dependent dielectric response indicates three relaxations processes in the dynamic window of modulus formalism. Variable range hopping model of small polarons manifests the bulk conduction mechanism. The bulk and grain boundary contributions have been estimated using impedance spectroscopy analysis and reveal that localized process dominates the relaxation. The direct evidence of glassy feature is established below 200 K by aging experiments. Our findings provide a potential connection between nearly constant loss features appearing below 200 K with fastest relaxation of magnitude 0.16 eV. We also discuss the time temperature superposition behavior using modulus scaling. A pressure driven normal ferroelectric to relaxor behavior is witnessed above a critical pressure as a result of relative competition between short range and long range forces. Our findings focus the role of high pressure as a fundamental bridge between normal ferroelectrics and relaxors. Intriguingly, there exists a direct connection between chemical pressure induced by substitution and external hydrostatic pressure. These findings have robust fundamental importance on theoretical elucidation of relaxation dynamics in perovskite systems., Comment: 29 pages, 8 figures

Published
2016

6. Fragility and Tendency to Crystallization for Structurally Related Compounds.

Author

Grzybowska, Katarzyna, Wojnarowska, Zaneta, Grzybowski, Andrzej, and Paluch, Marian

Subjects
*BROADBAND dielectric spectroscopy, *CRYSTALLIZATION, *CHEMICAL structure, *DIFFERENTIAL scanning calorimetry, *HEAT capacity, *CRYSTALLIZATION kinetics
Abstract

The present study was designed to investigate the physical stability of three organic materials with similar chemical structures. The examined compounds revealed completely different crystallization tendencies in their supercooled liquid states and were classified into three distinct classes based on their tendency to crystallize. (S)-4-Benzyl-2-oxazolidinone easily crystallizes during cooling from the melt; (S)-4-Benzylthiazolidine-2-thione does not crystallize during cooling from the melt, but crystallizes easily during subsequent reheating above Tg; and (S)-4-Benzyloxazolidine-2-thione does not crystallize either during cooling from the melt or during reheating. Such different tendencies to crystallize are observed despite the very similar chemical structures of the compounds, which only differ in oxide or sulfur atoms in one of their rings. We also studied the isothermal crystallization kinetics of the materials that were shown to transform into a crystalline state. Molecular dynamics and thermal properties were thoroughly investigated using broadband dielectric spectroscopy, as well as conventional and temperature-modulated differential scanning calorimetry in the wide temperature range. It was found that all three glass formers have the same dynamic fragility (m = 93), calculated directly from dielectric structural relaxation times. This result verifies that dynamic fragility is not related to the tendency to crystallize. In addition, thermodynamic fragility predictions were also made using calorimetric data. It was found that the thermodynamic fragility evaluated based on the width of the glass transition, observed in the temperature dependence of heat capacity, correlates best with the tendency to crystallize. [ABSTRACT FROM AUTHOR]

Published
2024
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11. Temperature- and pressure-induced structural changes of cobalt(II) in a phosphonium-based ionic liquid

Author

McCourt, Eadaoin, Wojnarowska, Zaneta, Jacquemin, Johan, Nockemann, Peter, Manyar, Haresh G., Hawełek, Łukasz, and Paluch, Marian

Subjects
cobalt complexes, Ionic liquids
Abstract

In this paper the temperature and pressure induced paramagnetic switching of cobalt (II) complex in binary mixture of phosphonium based ionic liquid [P6,6,6,14]SCN and [Co(NCS)2], is reported. This arises from a structural change in the coordination of the cobalt (II) center from tetrahedral [Co(NCS)4]2- to octahedral [Co(NCS)6]4- when mobile thiocyanate ions are added. These properties are reflected in the abrupt change of conductivity behavior of the magnetic ionic liquid. Therefore, as demonstrated herein the reversible switching in coordination of cobalt from tetrahedral to octahedral can be easily monitored at ambient as well as elevated pressure by tracking the dc-conductivity changes.

Published
2016
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14. Effect of polymer structure on the molecular dynamics and thermal behavior of poly(allyl acetoacetate) and copolymers

Author

Grzybowska, Katarzyna, Wojnarowska, Zaneta, Grzybowski, Andrzej, Paluch, Marian, Giussi, Juan M., Cortizo, M. Susana, Blaszczyk-Lezak, Iwona, Mijangos, Carmen, Grzybowska, Katarzyna, Wojnarowska, Zaneta, Grzybowski, Andrzej, Paluch, Marian, Giussi, Juan M., Cortizo, M. Susana, Blaszczyk-Lezak, Iwona, and Mijangos, Carmen

Abstract

In this paper, dielectric and calorimetric studies of the small-molecule glass former allyl acetoacetate monomers as well as its newly synthetized homopolymer and copolymers with different styrene composition were performed in both the liquid and glassy states. The molecular dynamics studies by the broadband dielectric spectroscopy and the stochastic temperature modulated differential scanning calorimetry enabled us to explore relaxation processes of examined materials in the wide frequency range. We found that the copolymers reveal two co-existing glass transitions characterized by the glass transition temperatures, which are very close to those of the corresponding homopolymers. These results suggest that the copolymers exhibited some sequences of acetoacetate units with a microphase-separated morphology in agreement with the value of reactivity ratio previously determined. We investigated effects of copolymerization compositions on the glass transition temperature, the isobaric fragility index, the dielectric and calorimetric intensity, and the dynamic heterogeneity on the glass transitions of the materials.

Published
2014

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