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  • 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. - 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.
  • Karlsson, M., et al. (författare)
  • Short-range structure of proton-conducting BaM0.10Zr0.90O2.95 (M = Y, In, Sc and Ga) investigated with vibrational spectroscopy
  • 2010
  • Ingår i: Solid State Ionics. - : Elsevier. - 0167-2738 .- 1872-7689. ; 181:3-4 (Sp. Iss.), s. 126-129
  • Tidskriftsartikel (refereegranskat)abstract
    • The short-range structures of hydrated and dry samples of the proton-conducting, cubic-structured, acceptor-doped perovskites BaM0.10Zr0.90O2.95 (M=Y, In, Sc and Ga), and, for comparison, BaZrO3, have been investigated using infrared and Raman spectroscopy. The results show that the acceptor-doping leads to local structural distortions of the average cubic structure, most likely related to tilts of (M/Zr)O-6 octahedra, and that the distortions are most pronounced in the Ga-doped material for which we also find additional distortions upon hydration. For the Y-, In- and Sc-doped equivalents the distortions are somewhat weaker and hydration is found to have a reversed, although weak, effect. A comparison of the spectroscopic results to the reported proton diffusivities of the investigated materials would suggest that the much lower proton diffusivity in the Ga-doped material is associated to its stronger structural distortions. (C) 2009 Elsevier B.V. All rights reserved.
  • Karlsson, Maths, 1978, et al. (författare)
  • Short-range structure of proton-conducting perovskite BaInxZr1-xO3-x/2 (x=0-0
  • 2009
  • Ingår i: Chemistry of Materials. - 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.
  • Karlsson, Maths, 1978, et al. (författare)
  • Structural Origin of the Mixed Glass Former Effect in Sodium Borophosphate Glasses Investigated with Neutron Diffraction and Reverse Monte Carlo Modeling
  • 2015
  • Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 119:49, s. 27275-27284
  • Tidskriftsartikel (refereegranskat)abstract
    • The mixed glass former systems 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - x)P2O5] and 0.5Na(2)O + 0.5[xB(2)O(3) + (1 - x)P2O5] with x = 0-1 were investigated with neutron diffraction (ND) together with reverse Monte Carlo (RMC) modeling of 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - x)P2O5]. The results show that the structure of both systems is reflected by an intermediate-range ordering, with a characteristic x-dependent length scale of about 4-6 angstrom and which contracts slightly with the increase of the Na concentration. Results obtained from RMC modeling of the 0.35Na(2)O + 0.65[xB(2)O(3) + (1 - x)P2O5] system, using both previously reported X-ray diffraction (XRD) data as well as the here obtained ND data as independent constraints in the modeling, show that the intermediate-range structural features, notably the Na coordination and volume fraction of the conducting pathways, are only weakly dependent on the choice of the constraints used. In particular, we observe that the volume fraction of the conducting pathways and the activation energy for ionic conduction are only weakly correlated to each other, as opposed to what is found for binary alkali borate and phosphate glasses.
  • Karlsson, Maths, 1978, et al. (författare)
  • Structure of Proton-Conducting Alkali Thio-Hydroxogermanates
  • 2008
  • Ingår i: Chemistry of Materials. - : The 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.
  • Karlsson, Maths, 1978, et al. (författare)
  • Temperature-Dependent Infrared Spectroscopy of Proton-Conducting Hydrated Perovskite BaInxZr1-xO3-x/2 (x=0.10-0.75)
  • 2010
  • Ingår i: Journal of Physical Chemistry C. - : The American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:13, s. 6177-6181
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the temperature dependence of the O-H stretch band in the infrared absorbance spectra of the proton-conducting hydrated perovskites BaInxZr1-xO3-x/2 (x = 0.10-0.75) over the temperature range -160 to 350 degrees C. Upon increasing temperature from -160 to 30 degrees C, we show that there is a redistribution of protons from nonsymmetrical structural configurations, such as Zr-OH-In and Zr-OH-Zr-vacancy, where the degree of hydrogen bonding between the protons and neighboring oxygens is strong, to symmetrical configurations, such as Zr-OH-Zr and In-OH-In, where hydrogen bonding is weaker. Spectra measured at elevated temperatures, 30-350 degrees C, indicate preferential desorption of protons in sites where the degree of hydrogen bonding is strong, and show that the materials gradually dehydrate with increasing temperature. The dehydration rate is found to be highest in the temperature range 275-325 degrees C. Furthermore, the spectroscopic results indicate that strong hydrogen bonding, caused by dopant-induced short-range structural distortions, is favorable for high proton mobility and that the rate-limiting step in the conduction mechanism is the proton transfer between neighboring oxygens.
  • Karlsson, Maths, 1978, et al. (författare)
  • Using Neutron Spin-Echo To Investigate Proton Dynamics in Proton-Conducting Perovskites
  • 2010
  • Ingår i: Chemistry of Materials. - : The American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 22:3, s. 740-742
  • Tidskriftsartikel (refereegranskat)abstract
    • The applicability and potential of neutron spin-echo (NSE) to study proton dynamics in proton-conducting ceramics was studied. The experiment was performed on hydrated BaZr 0,90 Y 0.10 O 2.95 (10Y:BZO), a cubic perovskite with a relatively high proton conductivity. The NSE experiment was performed at the IN15 spectrometer at Institut Laue-Langevin (ILL) in Grenoble, France. The relaxation rate for two Q-values for the temperature 563 K was determined. The first-principles calculations were carried out within the framework of density functional theory (DFT). The calculated diffusion harriers far from Y-dopants are found to he 0.20 and 0.18 eV for the proton transfer and hydroxyl rotation motion, respectively. The binding energy to a Y-dopant is 0.16 eV, and the influence of the Y-dopant on the energetics for the proton is quite extended in space, including both the first and the second coordination shells.
  • 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. - 1098-0121. ; 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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