| 1. |
- Andreasson, Jakob, 1975, et al.
(författare)
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Electron-phonon interactions in perovskites containing Fe and Cr studied by Raman scattering using oxygen-isotope and cation substitution
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 78:23, s. 235103-
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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.
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| 2. |
- Azad, Abul Kalam, 1966, et al.
(författare)
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Electron doping effect on structural and magnetic phase transitions in Sr2-xNdxFeMoO6 double perovskites
- 2006
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 179:5, s. 1303-1311
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline Sr2−xNdxFeMoO6 (x=0.0, 0.1, 0.2, 0.4) materials have been synthesized by a citrate co-precipitation method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature-dependent NPD data shows that the compounds (x=0.0, 0.1, 0.2) crystallize in the tetragonal symmetry in the range 10–400 K and converts to cubic symmetry above 450 K. The unit cell volume increases with increasing Nd3+ concentration, which is an electronic effect in order to change the valence state of the B-site cations. Antisite defects at the Fe–Mo sublattice increases with the Nd3+ doping. The Curie temperature was increased from 430 K for x=0 to 443 K for x=0.4. The magnetic moment of the Fe-site decreases while the Mo-site moment increases with electron doping. The antiferromagnetic arrangement causes the system to show a net ferrimagnetic moment.
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| 3. |
- Biendicho, Jordi Jacas, et al.
(författare)
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New in-situ neutron diffraction cell for electrode materials
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 248, s. 900-904
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Tidskriftsartikel (refereegranskat)abstract
- A novel neutron diffraction cell has been constructed to allow in-situ studies of the structural changes in materials of relevance to battery applications during charge/discharge cycling. The new design is based on the coin cell geometry, but has larger dimensions compared to typical commercial batteries in order to maximize the amount of electrode material and thus, collect diffraction data of good statistical quality within the shortest possible time. An important aspect of the design is its modular nature, allowing flexibility in both the materials studied and the battery configuration. This paper reports electrochemical tests using a Nickel-metal-hydride battery (Ni-MH), which show that the cell is able to deliver 90% of its theoretical capacity when using deuterated components. Neutron diffraction studies performed on the Polaris diffractometer using nickel metal and a hydrogen-absorbing alloy (MH) clearly show observable changes in the neutron diffraction patterns as a function of the discharge state. Due to the high quality of the diffraction patterns collected in-situ (i.e. good peak-to-background ratio), phase analysis and peak indexing can be performed successfully using data collected in around 30 min. In addition to this, structural parameters for the beta-phase (charged) MH electrode obtained by Rietveld refinement are presented. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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| 4. |
- Eriksson, Annika, 1975, et al.
(författare)
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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
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Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558. ; 11:11, s. 1945-1954
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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.
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| 5. |
- Eriksson, Annika, 1975, et al.
(författare)
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High temperature phase transition of the magnetoelectric double perovskite Sr2NiMoO6 by neutron diffraction
- 2006
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Ingår i: Materials Research Bulletin. - 0025-5408. ; 41, s. 144-157
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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.
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| 6. |
- Eriksson, Annika, 1975, et al.
(författare)
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Influence of iron addition on the oxygen-deficient Sr0.85Bi0.15Co1-xFexO3-d (0.0
- 2008
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Ingår i: Journal of Solid state chemistry. - 0022-4596 .- 1095-726X. ; 181, s. 2031-2040
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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.
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| 7. |
- Eriksson, Annika, 1975, et al.
(författare)
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Phase stability study of Bi0.15Sr0.85-xAexCoO3-δ (x = 0 and Ae = Ba0.28; Ca0.17) perovskites by in-situ neutron diffraction
- 2010
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Ingår i: Materials Research Bulletin. - : Elsevier BV. - 0025-5408. ; 45:12, s. 1875-1882
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Tidskriftsartikel (refereegranskat)abstract
- The oxygen deficient perovskites, Bi0.15Sr0.85-xAexCoO3-δ, x = 0 and Aex = Ba0.28, Ca0.17, were studied with in-situ neutron powder diffraction and combined TGA/DSC in order to investigate their behaviour at elevated temperatures in oxidising conditions. The phase stability of the I4/mmm supercell structure adopted by Bi0.15Sr0.85CoO3-δ is shown to be dependent on temperature and the oxygen content of the phase, with three structural events, at T 250, 590 and 880 °C, detected. The first transition occurs as the perovskite supercell vanishes due to oxygen absorption; the second transition is also associated with oxidation and involves the decomposition of the perovskite phase via an exothermic process to yield a dominant hexagonal phase. Finally, at T 900 °C the perovskite phase re-forms. For the Ba and Ca containing materials the decomposition to the hexagonal phase occurs at T 600 °C and 650 °C respectively. The presence of Ca at the A-site is found to stabilise the I4/mmm supercell structure in the range RT - 650 °C. The antiferromagnetic to paramagnetic transitions occur at TN 250 °C, TN 175 °C and TN 145 °C for the samples with Aex = Ba0.28, x = 0 and Aex = Ca0.17, respectively.
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| 8. |
- Eriksson, AK, et al.
(författare)
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Phase transitions of the magnetoelectric A(2)NiMoO(6) (A = Ba, Sr) and Ca2NiWO6 by neutron diffraction
- 2006
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Ingår i: FERROELECTRICS 339: 1921-+ 2006.
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Tidskriftsartikel (refereegranskat)abstract
- The magneticferroelectric double perovskites A(2)NiMoO(6) (A = Ba, Sr), and Ca2NiWO6 have been characterised using neutron powder diffraction (NPD) data. The Ba2NiMoO6 compound has previously been reported in cubic or hexagonal symmetry which led to investigation of polymorphism. High temperature NPD data of the Sr2NiMoO6 compound indicates a continuous structural phase transition from tetragonal to cubic symmetry at approximately 550 K. The reduction in symmetry is linked to spontaneous polarization allowing the structural perturbation to be described as an improper ferroelectric phase transition. The Ca2NiWO6 compound shows similar behaviour as Sr2NiMoO6 above 700 K, possibly P2(I)/n -> (I2/m) -> 14/m -> Fm-3m.
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| 9. |
- Malmgren, Christine, et al.
(författare)
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Nanocrystallinity in RuO2 coatings-Influence of precursor and preparation temperature
- 2010
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 518:14, s. 3615-3618
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Tidskriftsartikel (refereegranskat)abstract
- The effects of precursor and calcination temperature on the nano morphology of ruthenium dioxide on titanium, prepared from thermal decomposition of aqueous salt solutions were investigated. Transmission electron microscopy. X-ray diffraction, gas porosimetry and cyclic voltammetry showed that lower calcination temperature yielded smaller crystallites. The crystallites were between 6 and 22 nm in diameter. When using ruthenium nitrosyl nitrate the firing temperature had a large impact on the grain size, but for chloride there was only a minor effect in the temperature range 350-550 degrees C.
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| 10. |
- Slawinski, Wojciech Andrzej, 1980, et al.
(författare)
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Neutron Pair Distribution Function Study of FePO4 and LiFePO4
- 2019
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 31:14, s. 5024-5034
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Tidskriftsartikel (refereegranskat)abstract
- Neutron powder diffraction studies of the compounds FePO4 and LiFePO4 are reported. Rietveld refinement of the diffraction data provides averaged structures for both materials that are in good agreement with the published structures. In addition, detailed investigations of the short-range ion-ion correlations within each compound have been performed using the reverse Monte Carlo (RMC) modeling of the total scattering (Bragg plus diffuse) data. Although the short-range structural information for LiFePO4 is consistent with the long-range (averaged) picture, a small, but statistically significant, proportion of the anions is displaced away from their ideal sites within the RMC configurations of FePO4. These anion displacements are discussed in terms of a small concentration of Li+/Fe2+ occupying the empty octahedral sites, probably arising from incomplete delithiation of the LiFePO4 and/or antisite (Li+-Fe2+) defects introduced during the delithiation process.
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