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- Eriksson, Annika, 1975, et al.
(author)
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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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In: Solid State Sciences. - : Elsevier BV. - 1293-2558. ; 11:11, s. 1945-1954
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Journal article (peer-reviewed)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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- Eriksson, A K, et al.
(author)
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Effets of A-site substitution on the structure and magnetic properties of Bi0.15Sr0.85-yAeyCo1-xFexO3-o
- 2009
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In: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 11:11, s. 1945-1954
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Journal article (peer-reviewed)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 <= x <= 1.0, have been investigated. The differing ionic size of the Ca2+ and Ba2+ cations influences both the crystal structure and the properties of the materials. The smaller Ca2+ cation favoured formation of an oxygen vacancy ordered perovskite superstructure (14/mmm, a = 2ap, c = 4a(p)), meanwhile the presence of the larger Ba2+ cation promoted a disordered simple cubic structure (Pm (3) over barm, a = ap) that was also found for all Fe containing samples, i.e. x >= 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.
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- Galati, R., et al.
(author)
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Hydration, Structure, and Superconductivity of KOs2O6·nH2O
- 2008
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:4, s. 1652-1659
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Journal article (peer-reviewed)abstract
- In moist air or by contact with water during washing, KOs2O6 absorbs water molecules into the structure to produce KOs2O6·nH2O, 0 < n < 0.1. This water is reversibly lost on heating above ∼430 K in flowing or static gas environments. Variable temperature powder neutron and X-ray diffraction show that an increase in lattice parameter occurs when water enters the pyrochlore structure and the water molecules are located in the α cages displacing a portion of the potassium ions to adjacent sites. On removing water the lattice parameter and structure revert to those of the normal β-pyrochlore crystallographic description. Hydration has the effect of reducing the onset of superconducting behavior from a critical temperature of 10.25 K in fully dry KOs2O6 to 9.75 K in KOs2O6·0.1H2O.
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- Kalland, L. E., et al.
(author)
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C-type related order in the defective fluorites La2Ce2O7 and Nd2Ce2O7 studied by neutron scattering and ab initio MD simulations
- 2016
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 18:34, s. 24070-24080
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Journal article (peer-reviewed)abstract
- This work presents a structural investigation of La2-xNdxCe2O7 (x = 0.0, 0.5, 1.0, 1.5, 2.0) using X-ray powder diffraction and total scattering neutron powder diffraction, analysed using Rietveld and the reverse Monte Carlo method (RMC). Ab initio molecular dynamics (MD) modelling is also performed for further investigations of the local order. The main intensities in the neutron diffraction data for the La2-xNdxCe2O7 series correspond to the fluorite structure. However, additional C-type superlattice peaks are visible for x > 0 and increase in intensity with increasing x. The Nd-containing compositions (x > 0) are best fitted with Rietveld analysis by using a combination of oxygen deficient fluorite and oxygen excess C-type structures. No indications of cation order are found in the RMC or Rietveld analysis, and the absence of cation order is supported by the MD modelling. We argue that the superlattice peaks originate from oxygen vacancy ordering and associated shift in the cation position away from the ideal fluorite site similar to that in the C-type structure, which is seen from the Rietveld refinements and the observed ordering in the MD modelling. The vacancies favour alignments in the , and especially the direction. Moreover, we find that such ordering might also be found to a small extent in La2Ce2O7, explaining the discernible modulated background between the fluorite peaks. The observed overlap of the main Bragg peaks between the fluorite and C-type phase supports the co-existence of vacancy ordered and more disordered domains. This is further supported by the observed similarity of the radial distribution functions as modelled with MD. The increase in long range oxygen vacancy order with increasing Nd-content in La2-xNdxCe2O7 corresponds well with the lower oxide ion conductivity in Nd2Ce2O7 compared to La2Ce2O7 reported earlier.
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- KINYANJUI, FRANCIS GACHAO, 1981, et al.
(author)
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Crystal structure and proton conductivity of BaSn0.6Sc0.4O3-delta: insights from neutron powder diffraction and solid-state NMR spectroscopy
- 2016
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:14, s. 5088-5101
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Journal article (peer-reviewed)abstract
- The solid-state synthesis and structural characterisation of perovskite BaSn(1-x)ScxO(3-delta)(x = 0.0, 0.1, 0.2, 0.3, 0.4) and its corresponding hydrated ceramics are reported. Powder and neutron X-ray diffractions reveal the presence of cubic perovskites (space group Pm (3) over barm) with an increasing cell parameter as a function of scandium concentration along with some indication of phase segregation. Sn-119 and Sc-45 solid-state NMR spectroscopy data highlight the existence of oxygen vacancies in the dry materials, and their filling upon hydrothermal treatment with D2O. It also indicates that the Sn4+ and Sc3+ local distribution at the B-site of the perovskite is inhomogeneous and suggests that the oxygen vacancies are located in the scandium dopant coordination shell at low concentrations (x = 0.3). O-17 NMR spectra on O-17 enriched BaSn1-xScxO3-delta materials show the existence of Sn-O-Sn, Sn-O-Sc and Sc-O-Sc bridging oxygen environments. A further room temperature neutron powder diffraction study on deuterated BaSn0.6Sc0.4O3-delta refines the deuteron position at the 24k crystallographic site (x, y, 0) with x = 0.579(3) and y = 0.217(3) which leads to an O-D bond distance of 0.96(1) angstrom and suggests tilting of the proton towards the next nearest oxygen. Proton conduction was found to dominate in wet argon below 700 degrees C with total conductivity values in the range 1.8 x 10(-4) to 1.1 x 10(-3) S cm(-1) between 300 and 600 degrees C. Electron holes govern the conduction process in dry oxidizing conditions, whilst in wet oxygen they compete with protonic defects leading to a wide mixed conduction region in the 200 to 600 degrees C temperature region, and a suppression of the conductivity at higher temperature.
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