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Sökning: WFRF:(Matic Aleksandar 1968) > (2005-2009)

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14.
  • Karlsson, Maths, 1978, et al. (författare)
  • Quasielastic neutron scattering of hydrated BaZr0.90A0.10O2.95 (A = Y and Sc)
  • 2009
  • Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 180:1, s. 22-28
  • Tidskriftsartikel (refereegranskat)abstract
    • Proton motions in hydrated proton conducting perovskites BaZr 0.90 A 0.10 O 2.95 (A = Y and Sc) have been investigated using quasielastic neutron scattering. The results reveal a localized motion on the ps time scale and with an activation energy of ~ 10-30 meV, in both materials. The temperature dependence of the total mean square displacement of the protons shows an onset of this motion at a temperature of about 300 K. The low activation energy, much lower than the activation energy for the macroscopic proton conductivity, suggests that this motion is not the rate-limiting process for the long-range proton diffusion, i.e. it is not linked to the two materials significantly different proton conductivities. In fact, a comparison of the QENS results with density functional theory calculations indicates that for both materials the observed motion may be ascribed to intra-octahedral proton transfers occurring close to a dopant atom. © 2008 Elsevier B.V. All rights reserved.
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15.
  • Karlsson, Maths, et al. (författare)
  • Short-range structure of proton-conducting perovskite BaInxZr1-xO3-x/2 (x=0-0
  • 2009
  • Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:10, s. 3480-3486
  • Tidskriftsartikel (refereegranskat)abstract
    • In a systematic study, we investigate the effect of dopant level and hydration on the short-range structure of the proton-conducting perovskite-type oxide BaInxZr1-xO3-x/2 (x = 0 - 0.75), using infrared and Raman spectroscopy. The results show that the doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75, new bands appear and grow in intensity in both the IR and the Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size and charge difference between the In3+ and Zr4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O-6 octahedra. On the basis of our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the structural distortions propagate throughout the whole perovskite structure. Comparison of our spectroscopic data with the proton conductivity for the same materials indicates that the presence of extended structural distortions is favorable for fast proton transport.
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16.
  • Karlsson, Maths, 1978, et al. (författare)
  • Structure of Proton-Conducting Alkali Thio-Hydroxogermanates
  • 2008
  • Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 20:19, s. 6014-6021
  • Tidskriftsartikel (refereegranskat)abstract
    • Using a combination of neutron diffraction, infrared spectroscopy, and first-principles calculations, we have investigated the structure of hydrated and dehydrated proton conducting alkali thio-hydroxogermanates of general formula M2GeS2(OH)2·yH2O (M = K, Rb, and Cs). The results show that the structure of hydrated and dry materials are basically the same, which confirms previous indications that the main effect of heating these materials is just a loss of water. We suggest that in the hydrated state the structure of these materials is built of dimers of thio-hydroxogermanate anions, with the water molecules acting as bridges between such dimers. In the dehydrated structure, the thio-hydroxogermanate anions instead form an extended network through the formation of interdimer hydrogen bonds through the −OH groups in the structure. The alkali ions are suggested to act as “space-fillers” in voids formed by the thio-hydroxogermanate anion dimers, in both the hydrated and the dehydrated state.
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  • Karlsson, Maths, 1978, et al. (författare)
  • Vibrational Properties of Protons in Hydrated BaInxZr1-xO3-x/2
  • 2005
  • Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 72, s. 1-7
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the local proton dynamics in the proton conducting hydrated perovskite system BaInxZr1-xO3-x/2 (x=0.25-0.75) using infrared spectroscopy and first-principles calculations. We show that oxygen vacancies and dopant atoms in the vicinity of the proton tilt the proton toward a neighboring oxygen creating strongly hydrogen-bonded configurations. This is manifested as a strong redshift of the O-H stretch band in the infrared absorption spectrum. We also find considerable fluctuations of the nearest and next-nearest oxygen-proton distances with time, resulting in additional spectral broadening. By comparing the frequencies of computed O-H stretch modes we can relate specific local configurations to different parts of the broad O-H stretch band. Even though hydrogen-bonded configurations favor proton transfer they hinder the long-range migration by decreasing the reorientational rate. Thus, in order to optimize the proton mobility it is important to avoid extreme configurations caused by either oxygen vacancies or dopant atoms in the perovskite structure.
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20.
  • Martinelli, Anna, 1978, et al. (författare)
  • A structural study on ionic-liquid-based polymer electrolyte membranes
  • 2007
  • Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 154:8, s. G183-G187
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated novel proton conducting membranes synthesized through the gelification of poly(vinylidene fluoride-co-hexafluoropropylene) in aprotic ionic liquids. Mobile protons were introduced by doping the system with the strong bis(trifluoromethanesulfonyl)imide acid (HTFSI), which is chemically compatible with the ionic liquids through the common TFSI- anion. The obtained membranes are thermally stable up to 115°C set by the melting of the polymer phase. At this temperature, the conductivity is on the order of 10-2 S cm-1. Raman and infrared spectroscopy show no chemical interactions between the components, indicating that the bulklike nature of the doped ionic liquids preserved within the membrane, as is the thermal stability and the high conductivity. © 2007 The Electrochemical Society.
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