| 1. |
- Andreasson, Jakob, 1975, et al.
(författare)
-
Franck-Condon higher order lattice excitations in the LaFe(1-x)Cr(x)O3 (x=0, 0.1, 0.5, 0.9, 1.0) perovskites due to Fe-Cr charge transfer effects
- 2007
-
Ingår i: Physical Review B. ; 75, s. 104302-
-
Tidskriftsartikel (refereegranskat)abstract
- First and higher order lattice excitiations in the B-site disordered perovskites LaFe(1-x)Cr(x)O3 (x = 0, 0.1, 0.5, 0.9, 1) and La(0.835)Sr(0.165)Fe(0.5)Cr(0.5)O(3-d) are investigated using temperature dependent and polarised inelastic light scattering [lambda = 515 nm (2.41 eV) and 676 nm (1.83 eV)] on oriented crystallites.A peak at approximately 2.4 eV in the imaginary part of the dielectric function of LaFe(0.5)Cr(0.5)O3 is assigned to a charge transfer from Fe 3+ (d5) to Cr 3+ (d3) ions and coupled the appearance of an intense Ag-like mode at approximately 700 cm-1 in the Raman data. This excitation is identified as a symmetric oxygen breathing mode activated by the Fe-Cr charge transfer through an orbital coupling mechanism. Higher order scattering (up to 7th order) of the intrinsic Raman active symmetric breathing mode is also explained by an orbital mediated, electron-phonon coupling, similar to the Franck-Condon effect observed in the Jahn-Teller active perovskite structured manganite LaMnO3. These results show that the Franck-Condon mechanism is a more common mechanism for resonant higher order scattering in solids than previously believed and propose the LaFe(1-x)Cr(x)O(3) system as a model system for electron-phonon coupling and higher order Raman scattering in solids.
|
|
| 2. |
- Johansson, Malin E V, 1971, et al.
(författare)
-
Composition and functional role of the mucus layers in the intestine.
- 2011
-
Ingår i: Cellular and Molecular Life Sciences. - : Springer Science and Business Media LLC. - 1420-682X .- 1420-9071. ; 68, s. 3635-3641
-
Forskningsöversikt (refereegranskat)abstract
- In discussions on intestinal protection, the protective capacity of mucus has not been very much considered. The progress in the last years in understanding the molecular nature of mucins, the main building blocks of mucus, has, however, changed this. The intestinal enterocytes have their apical surfaces covered by transmembrane mucins and the whole intestinal surface is further covered by mucus, built around the gel-forming mucin MUC2. The mucus of the small intestine has only one layer, whereas the large intestine has a two-layered mucus where the inner, attached layer has a protective function for the intestine, as it is impermeable to the luminal bacteria.
|
|
| 3. |
|
|
| 4. |
- Bäckström, Joakim, 1971
(författare)
-
Raman Scattering and Neutron Diffraction Studies of Manganites and Cuprates
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to experimental studies of two classes of strongly correlated transition metal oxides, namely cuprates and manganite perovskites. Manganites generally display complex phase diagrams, including the so-called colossal magnetoresistance effect. Some cuprates show high-temperature superconductivity, a phenomenon that is poorly understood in spite of many years of intense research. It is clear, though, that a delicate interplay between the atomic structure, magnetism and charge carriers is important in these materials. Experimental investigations have been done using Raman spectroscopy, a powerful technique for these studies since it is able to simultaneously probe vibrational, magnetic and electronic excitations. Neutron diffraction in combination with Reverse Monte Carlo modelling have been used to study both structural and magnetic ordering on a local scale. We demonstrate that an anomaly of the Ba-phonon mode in YBa2Cu4O8 is directly correlated to the opening of a pseudogap well above the superconducting critical temperature. A similar anomaly in the non-superconductor PrBa2Cu4O8 indicates that the pseudogap state is not a sufficient prerequisite for superconductivity. Following neutron diffraction studies of PrBa2Cu4O8 reveal a Ba-site instability, which we link to anomalies in the electronic properties. In the high-temperature superconductor YBa2Cu3O6+x, we investigate the influence of light irradiation on the Raman spectra and propose a simplistic model for photoinduced effects. We show effects of interactions between charge and lattice degrees of freedom in the manganites La0.5Ca0.5MnO3 and La1-xSrxMnO3. In the latter compound, we discovered a low-energy electronic excitation suggesting the existence of a two-component metallic state.
|
|
| 5. |
- Iliev, M. N., et al.
(författare)
-
Comparative Raman studies of Sr2RuO4, Sr 3Ru2O7 and Sr4Ru3O 10
- 2005
-
Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 358:1-4, s. 138-152
-
Tidskriftsartikel (refereegranskat)abstract
- The polarized Raman spectra of layered ruthenates of the Srn+1RunO3n+1 (n=1,2,3) Ruddlesden-Popper series were measured between 10 and 300 K. The phonon spectra of Sr3Ru2O7 and Sr4Ru3O10 confirmed earlier reports for correlated rotations of neighboring RuO6 octahedra within double or triple perovskite blocks. The observed Raman lines of Ag or B1g symmetry were assigned to particular atomic vibrations by considering the Raman modes in simplified structures with only one double or triple RuO6 layer per unit cell and by comparison to the predictions of lattice dynamical calculations for the real Pban and Pbam structures. Along with discrete phonon lines, a continuum scattering, presumably of electronic origin, is present in the zz, xx and xy, but not in the x′y′ and zx spectra. Its interference with phonons results in Fano shape for some of the lines in the xx and xy spectra. The temperature dependences of phonon parameters of Sr3Ru2O7 exhibit no anomaly between 10 and 300 K where no magnetic transition occur. In contrast, two B1g lines in the spectra of Sr4Ru3O10, corresponding to oxygen vibrations modulating the Ru-O-Ru bond angle, show noticeable hardening with ferromagnetic ordering at 105 K, thus indicating strong spin-phonon interaction.
|
|
| 6. |
- Näslund, Lars-Åke, et al.
(författare)
-
The Role of TiO2 Doping on RuO2-Coated Electrodes for the Water Oxidation Reaction
- 2013
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:12, s. 6126-6135
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical water splitting into H-2 and O-2 presents a significant and challenging energy loss due to the high overpotential required at the anode. Today, in industrially relevant applications, dimensionally stable anodes (DSA) based on the electrocatalytic active RuO2 are conventionally utilized. To enhance the resistance against corrosion, incorporation of TiO2 in the RuO2-coated electrodes is widely employed. In the present work we have used scanning electrochemical microscopy (SECM) to demonstrate that TiO2-doped RuO2-coated electrodes, in addition to being more durable, also show an electrocatalytic activity that is, on average, 13% higher as compared to the pure RuO2-coated electrodes. We also demonstrate that cracks in the pure RuO2 coating are the most active zones, probably because Ti from the Ti support has diffused into the first applied layer of the RuO2 coating. To reveal the nature of this enhanced activity for water oxidation displayed on TiO2-doped RuO2 electrodes, we have employed X-ray photoelectron spectroscopy (XPS) for material characterization. The results show that the electrocatalytic activity enhancement displayed on the mixed (Ru1-x:Ti-x)O-2 coating is promoted through a charge transfer from the RuO2 to the TiO2, which provides new and more reactive sites designated as activated RuO2 delta+.
|
|
