| 1. |
- Andreasson, Jakob, 1975, et al.
(författare)
-
Electron-phonon interactions in perovskites containing Fe and Cr studied by Raman scattering using oxygen-isotope and cation substitution
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 78:23, s. 235103-
-
Tidskriftsartikel (refereegranskat)abstract
- We use temperature-dependent inelastic light scattering to study the origin of the strong multiphonon scattering of a local oxygen breathing mode present in the mixed B-site orthorhombic (space group Pnma) perovskite LaFe0.5Cr0.5O3 but absent in isostructural LaFeO3 and LaCrO3. It is seen that the multiphonon scattering is critically sensitive to the presence of both Fe and Cr ions on the B site. These results support our interpretation that the multiphonon scattering is activated by local electron-phonon interactions according to the Franck-Condon picture following an Fe-Cr charge transfer. Further, O-18 substitution is performed on the x=0, 0.04, and 0.5 compounds and clearly shows that all modes appearing above the first-order phonon-scattering region in these compounds originate from higher-order oxygen stretching vibrations. In particular this is the case for the strong second-order scattering dominating the scattering response in LaFeO3. Accordingly we propose that these modes are generated by infrared-active longitudinal optical (IR LO) two-phonon and combination scattering activated by Frohlich interaction. For x=0.02 and 0.04 the characteristic IR LO two-phonon and Franck-Condon multiphonon-scattering profiles mix. We also study the influence of isovalent cation substitution and Sr doping in AFe(0.5)Cr(0.5)O(3) (A=La, Nd, and Gd) and La1-ySryFe0.5Cr0.5O3-delta (y=0, 0.16, and 0.5) on the strong electron-phonon coupling present in LaFe0.5Cr0.5O3. The Franck-Condon effect in LaFe0.5Cr0.5O3, is not significantly affected by isovalent A-site substitution, despite the increasing orthorhombic distortion associated with decreasing A-site ionic radii. On the contrary, aliovalent Sr doping causes a rapid decrease in the Franck-Condon scattering. This shows that the strong electron-phonon coupling in these compounds is highly sensitive to local lattice and electronic decoherence but insensitive to global lattice distortions. Finally, a preliminary assignment of the A(g) and B-2g phonon modes in AFe(0.5)Cr(0.5)O(3) (A=La, Nd, and Gd) is made based on the present observations and published results for LaCrO3 and AMnO(3). The modes associated with oxygen octahedral tilt and bending vibrations are heavily influenced by the magnitude of the orthorhombic distortion.
|
|
| 2. |
- Eriksson, Annika, 1975, et al.
(författare)
-
Effects of A-site substitution on the structure and magnetic properties of Bi(0.15)Sr(0.85-y)Ae(y)Co(1-x)Fe(x)O(3-delta) perovskites
- 2009
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558. ; 11:11, s. 1945-1954
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of partial substitution of Sr2+ by Ca2+ and Ba2+ on the A-site of oxygen-deficient perovskites, Bi(0.15)Sr(0.85-y)Ae(y)Co(1-x)FeO(3-delta), where y = 0.28 for Ae = Ba and y = 0.17 for Ae = Ca, and 0.0 = 0.25. The samples were studied with PXRD, NPD, TGA, electron microscopy and magnetic susceptibility measurements. All as-prepared samples exhibited long range G-type antiferromagnetic ordering. The effect of oxygen annealing was dramatic for the Bi0.15Sr0.68Ca0.17Co1-xFexO3-delta series, with a disappearance of magnetic order for x >= 0.25 linked to increasing spin-glass properties. The oxygen content of the Bi0.15Sr0.57Ba0.28Co1-xFexO3-delta as-prepared materials was generally higher than their Ca substituted counterparts, and the long range antiferromagnetic order was more resistant to oxygen annealing. (C) 2009 Elsevier Masson SAS. All rights reserved.
|
|
| 3. |
- Eriksson, Annika, 1975, et al.
(författare)
-
High temperature phase transition of the magnetoelectric double perovskite Sr2NiMoO6 by neutron diffraction
- 2006
-
Ingår i: Materials Research Bulletin. - 0025-5408. ; 41, s. 144-157
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic ferroelectric double perovskite Sr2NiMoO6 has been characterised using neutron powder diffraction (NPD) data and magnetic susceptibility measurements. High temperature NPD data indicate that the material undergoes a continuous structural phase transition from tetragonal (I4/m) to cubic (Fm(3) over barm) at approximately 550 K. The transition is linked to the level of rotation of the NiO6 and MoO6 octahedra, which form perfectly segregated sub-lattices in the material. The reduction in symmetry at 550 K is linked to the onset of a spontaneous dipole in the material allowing the structural perturbation to be described as an improper ferroelectric phase transition. The appearance of low angle reflections in the 20 K dataset indicates the presence of an antiferromagnetic ordered around state. The magnetic moment was refined to 1.88(8) mu(B) confirming that the magnetism originates from the Ni2+ (S = 1) ions. (C) 2005 Elsevier Ltd. All rights reserved.
|
|
| 4. |
- Eriksson, Annika, 1975, et al.
(författare)
-
Influence of iron addition on the oxygen-deficient Sr0.85Bi0.15Co1-xFexO3-d (0.0
- 2008
-
Ingår i: Journal of Solid state chemistry. - 0022-4596 .- 1095-726X. ; 181, s. 2031-2040
-
Tidskriftsartikel (refereegranskat)abstract
- A series of oxygen-deficient Sr0.85Bi0.15Co1-xFexO3-d (0.00.8. Evidence of weak superstructures, reflecting local oxygen ordering, is also obtained from electron diffraction. For all oxygen-annealed phases the average structure reverts to cubic Pm-3m. The as-prepared samples show G-type antiferromagnetic order at room temperature. The oxygen annealed x = 0.10, 0.25 and 1.0 samples display low-temperature spin-glass transitions.
|
|
| 5. |
- Casari, Barbara M., et al.
(författare)
-
New Aquapentachlorochromate(III) Compounds: K2[CrCl5(H2O)] and (NH4)2[CrCl5(H2O)]
- 2006
-
Ingår i: Zeitschrift für Anorganische und Allgemeine Chemie. - 0044-2313 .- 1521-3749. ; 632:1, s. 101-106
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis and crystal structures of two new compounds, K2[CrCl5(H2O)] (I) and (NH4)2[CrCl5(H2O)] (II) are reported. Both compounds were prepared from chromium(VI) salts by two different methods and reaction pathways of these syntheses are suggested. The crystal structures of these two aquapentachlorochromates(III) have been determined from three dimensional X-ray data collected at low temperature, 173 K. The two structures are isomorphous and their unit cell dimensions are quite similar. They are orthorhombic, space groups Pnma, with Z = 4. Both structures are composed of [CrCl5(H2O)]2- units held together by the counterion framework. The coordination around the chromium ion deviates from a regular octahedron due to the shorter equatorial chromium-oxygen bond.
|
|
| 6. |
- Casari, Barbara M., et al.
(författare)
-
Synthesis Methods for Ce(CrO4)2 · xH2O and Crystal Structures of K2CrSO7, (NH4)2Cr2O7 and Na2Cr2O7 · 2H2O
- 2007
-
Ingår i: Zeitschrift für Naturforschung - Section B Journal of Chemical Sciences. - 0932-0776. ; 62b:6, s. 771-777
-
Tidskriftsartikel (refereegranskat)abstract
- New and quick methods to synthesize Ce(CrO4)2 · 2H2O and Ce(CrO4)2 · H2O, giving high yields,are described. The methods are based on exchange reactions by refluxing in water or on solid statereactions. The first crystal structure containing a chromatosulfato ion is presented. K2CrSO7 belongsto space group P21/n with a=7.4024(1), b=7.3908(1), c=12.9883(2) Å , β=90.021(1)◦ and Z = 4.The CrSO72− ion, consisting of one chromate group sharing one oxygen atom with one sulfate group, has a pseudo syn-C2v conformation with eclipsed oxygen atoms. K2CrSO7 forms a three dimensional network of CrSO72− ions held together by the charge balancing potassium ions, with the generalstructural features common with dichromate-like structures. The redetermination of the structures of(NH4)2Cr2O7 (space group C2/c, with hydrogen atoms located) and Na2Cr2O7 · 2H2O (space group P21, with hydrogen atoms located and the absolute structure established) are reported.
|
|
| 7. |
|
|
| 8. |
- Eriksson, Annika, 1975
(författare)
-
Phase Transitions of the Magnetoelectric A2NiMoO6 (A = Ba, Sr) and Ca2NiWO6 by Neutron Diffraction
- 2006
-
Ingår i: Ferroelectrics. - 0015-0193. ; 339, s. 1921-
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic ferroelectric double perovskites A2NiMoO6 (A = Ba, Sr), and Ca2NiWO6have been characterised using neutron powder diffraction (NPD) data. The Ba2NiMoO6compound has previously been reported in cubic or hexagonal symmetry which led to investigationof polymorphism. High temperature NPD data of the Sr2NiMoO6 compoundindicates a continuous structural phase transition from tetragonal to cubic symmetry atapproximately 550 K. The reduction in symmetry is linked to spontaneous polarizationallowing the structural perturbation to be described as an improper ferroelectric phasetransition. The Ca2NiWO6 compound shows similar behaviour as Sr2NiMoO6 above700 K, possibly P21/n→(I2/m)→14/m→Fm-3m.
|
|
| 9. |
- Juhlin, Magnus, 1975-, et al.
(författare)
-
Aerodynamic loads on buses due to crosswind gusts – On-road measurements
- 2008
-
Ingår i: Vehicle System Dynamics. - : Taylor & Francis. - 0042-3114 .- 1744-5159. ; 46, s. 827-835
-
Tidskriftsartikel (refereegranskat)abstract
- Bus and coach traffic is considered to be one of the safest means of travelling. Still, there is a problem with accidents due to crosswind gusts. Therefore it is a need of improving the crosswind performance of buses. As a part of the work with improving the crosswind performance a method for estimating the aerodynamic loads on a bus when exposed to natural crosswind is proposed. The method is based on measurements of the vehicle response and the tire forces from which the aerodynamic loads are estimated using inverse simulations. The results are also shown to agree well with the results of other studies based on wind tunnel measurements. The estimated aerodynamic loads are intended to be used in a future study on crosswind sensitivity using a moving base simulator.
|
|
| 10. |
- Rehnberg, Adam, 1975-
(författare)
-
Vehicle dynamic analysis of wheel loaders with suspended axles
- 2008
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The wheel loader is a type of engineering vehicle used primarily to move crude material over shorter distances. As the vehicle is designed without wheel suspension, wheel loader drivers are exposed to high levels of whole body vibration which influences ride comfort negatively. The work presented in this thesis has the aim to investigate the potential in adding an axle suspension to a wheel loader in order to reduce vibrations and increase handling quality. While suspended axles have great potential for improving ride comfort and performance, they will also necessarily affect the vehicle dynamic behaviour which is different in many aspects from that of passenger cars or other road vehicles: the wheel loader has a large pitch inertia compared to its mass, the axle loads vary considerably with loading condition, and the vehicle uses an articulated frame steering system rather than wheel steering. These issues must all be considered in the design process for a wheel loader suspension. The effects of suspended axles on ride vibrations are analysed by simulating a multibody wheel loader model with and without axle suspension. Results from the simulations show that longitudinal and vertical acceleration levels are greatly reduced with axle suspension, but that the decrease in lateral acceleration is smaller. By reducing the roll stiffness lateral accelerations can be further reduced, although this may not be feasible because of requirements on handling stability. The pitching oscillation of the vehicle has also been studied as this is known to have a large influence on ride comfort. An analytical model is used to study the effect of front and rear suspension characteristics on the pitching response of the wheel loader, showing that a stiffer rear suspension is favourable for reducing pitching but also that a similar effect is attainable with a stiffer front suspension. Results are compared to multibody simulations which show the same trend as analytical predictions. By including a linearised representation of a hydropneumatic suspension in the models, it is also shown that favourable dynamic behaviour can be maintained when the vehicle is loaded by utilising the fact that suspension stiffness is increasing with axle load. Articulated vehicles may exhibit lateral oscillations known as "snaking" when driven at high speed. The effect of suspended axles on these oscillations are analysed using a multibody simulation model of a wheel loader with an equivalent roll stiffness suspension model. It is found that the roll motion of the sprung mass has a slightly destabilising effect on the snaking oscillations. This effect is more pronounced if the body roll frequency is close to the frequency of the snaking motion, although this loss in stability can be compensated for by increasing the equivalent stiffness or damping of the steering system. Together with existing vehicle dynamic theory and design rules, the studies reported in this work provide an insight into the specific issues related to suspension design for wheel loaders.
|
|
