| 1. |
- Biendicho, J. J., et al.
(författare)
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Synthesis and characterization of perovskite-type Sr(x)Y1-xFeO(3-delta) (0.63 <= x < 1.0) and Sr0.75Y0.25Fe1-yMyO3-delta (M=Cr, Mn, Ni), (y=0.2, 0.33, 0.5)
- 2013
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 200, s. 30-38
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-deficient ferrates with the cubic perovskite structure SrxY1-xFeO3-delta were prepared in air (0.71 <= x <= 0.91) as well as in N-2 (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-delta=2.79(2) for x=0.75 to 3-delta=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.25Y0.25FeO2.29 using TOP neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and highresolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along (1 0 0)(p) with G +/- similar to 0.4(1 0 0)(p) indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25Fe02.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm/K in air at 298-673 K. At 773-1173 K TEC increases up to 17.2 ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-delta (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25Fe02.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25Fe02.79.
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| 2. |
- Grins, J., et al.
(författare)
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A structural study of Ruddlesden-Popper phases Sr3-xYx(Fe125Ni075)O7-δ with x ≤ 0.75 by neutron powder diffraction and EXAFS/XANES spectroscopy
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6:13, s. 5313-5323
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Tidskriftsartikel (refereegranskat)abstract
- The structures of Ruddlesden-Popper n = 2 member phases Sr 3-x Y x Fe 1 25Ni0.75O 7-δ with 0 ≤ x ≤ 0.75 have been investigated using neutron powder diffraction and K-edge Fe and Ni EXAFS/XANES spectroscopy in order to gain information about the evolution of the oxygen vacancy distribution and Fe/Ni oxidation state with x. Both samples prepared at 1300°C under a flow of N 2 (g), with δ = 1.41-1.00, and samples subsequently annealed in air at 900°C, with δ = 0.44-0.59, were characterized. The as-prepared x = 0.75 phase has δ = 1, the O1 atom site is vacant, and the Fe 3+ /Ni 2+ ions have a square pyramidal coordination. With decreasing x the O3 occupancy decreases nearly linearly to 81% for x = 0, while the O1 occupancy increases from 0 for x = 0.4 to 33% for x = 0. The air-annealed x = 0.75 sample has a δ value of 0.59 and the Fe 3+ /Fe 4+ /Ni 2+ /Ni 3+ ions have both square pyramidal and octahedral coordination. With decreasing x, the δ value decreases to 0.45 for x = 0, implying an increase in the oxidation states of Fe/Ni ions. EXAFS/XANES data show that for the as-prepared samples the coordination changes are predominantly for Ni 2+ ions and that the air-annealed samples contain both Fe 3+ /Fe 4+ and Ni 2+ /Ni 3+ ions.
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| 3. |
- Rahman, Habibur Seikh Mohammad, 1976, et al.
(författare)
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Proton conductivity of hexagonal and cubic BaTi1-xScxO3-δ (0.1 ≤ x ≤ 0.8)
- 2014
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Ingår i: Dalton Transactions. - 1477-9226 .- 1477-9234. ; 43:40, s. 15055-15064
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Tidskriftsartikel (refereegranskat)abstract
- BaTi1−xScxO3−δ (x = 0.1–0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti4+ for Sc3+ gives a hexagonal perovskite structure, whereas high substitution (x = 0.5–0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H2O and D2O, conditions for BaTi1−xScxO3−δ (x = 0.2, 0.6 and 0.7). In the temperature range of 150–600 °C, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8Sc0.2O3−δ is approx. two orders of magnitude lower than that of the more heavily substituted cubic phases. Conductivity is also found to be higher in dry O2 than in Ar in the whole temperature range of 150–1000 °C, characteristic of a significant contribution from p-type charge carriers under oxidising atmospheres. Greater Sc3+ substitution leads to a higher proton concentration and the highest proton conductivity (σ [similar] 2 × 10−3 S cm−1 at 600 °C) is found for the BaTi0.3Sc0.7O3−δ composition.
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| 4. |
- Shafeie, Samrand, 1984, et al.
(författare)
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Crystal structure, thermal expansion and high-temperature electrical conductivity of A-site deficient La2-zCo1+y(MgxNb1-x)(1-y)O-6 double perovskites
- 2015
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 229, s. 243-251
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Tidskriftsartikel (refereegranskat)abstract
- New La-deficient double perovskites with P2(1)/n symmetry, La-similar to 1.90(Co1-x2+Mgx2+)(Co1/33+Nb2/35+)O-6 with x=0, 0.13 and 0.33, and La-2(Co1/22+Mg1/22+) (Co1/23+Nb1/25+)O-6 were prepared by solid state reaction at 1450 degrees C. Their crystal structures were refined using time-of-flight neutron powder diffraction data. Our results show that certain cations such as Nb5+, with very strong B-O bonds in the perovskite structure, can induce A-site vacancies in double perovskites. Upon heating in N-2 gas atmosphere at 1200 degrees C similar to 1% O atom vacancies are formed together with a partial reduction of the Co3+ content. The average thermal expansion coefficient between 25 and 900 degrees C of La-1.90(Co2/32+Mg1/32+)(Co1/33+Nb2/35+)O-6 was determined to be 17.4 ppm K-1. Four-point electronic conductivity measurements showed that the compounds are semiconductors, with conductivities varying between 3.7.10(-2) and 7.7.10(-2) S cm(-1) at 600 degrees C and activation energies between 0.77 and 0.81 eV. Partial replacement of La3+ with Sr2+ does not lead to any increase of conductivity, while replacement of Mg2+ with Cu2+ in La1.9CoCu1/3Nb2/3O6 and La1.8CoCu1/2Nb1/2O6 leads to similar to 100 times larger conductivities at 600 degrees C, 0.35 and 1.0 S cm(-1), respectively, and lower activation energies, 0.57 and 0.73 eV, respectively.
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| 5. |
- Grins, Jekabs, et al.
(författare)
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A structural study of Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta with x <= 0.75 by neutron powder diffraction and EXAFS/XANES spectroscopy
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6:13, s. 5313-5323
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Tidskriftsartikel (refereegranskat)abstract
- The structures of Ruddlesden-Popper n = 2 member phases Sr3-xYxFe1.25Ni0.75O7-delta with 0 <= x <= 0.75 have been investigated using neutron powder diffraction and K-edge Fe and Ni EXAFS/XANES spectroscopy in order to gain information about the evolution of the oxygen vacancy distribution and Fe/Ni oxidation state with x. Both samples prepared at 1300 degrees C under a flow of N-2(g), with delta = 1.41-1.00, and samples subsequently annealed in air at 900 degrees C, with delta = 0.44-0.59, were characterized. The as-prepared x = 0.75 phase has delta = 1, the O1 atom site is vacant, and the Fe3+/Ni2+ ions have a square pyramidal coordination. With decreasing x the O3 occupancy decreases nearly linearly to 81% for x = 0, while the O1 occupancy increases from 0 for x = 0.4 to 33% for x = 0. The air-annealed x = 0.75 sample has a delta value of 0.59 and the Fe3+/Fe4+/Ni2+/Ni3+ ions have both square pyramidal and octahedral coordination. With decreasing x, the delta value decreases to 0.45 for x = 0, implying an increase in the oxidation states of Fe/Ni ions. EXAFS/XANES data show that for the as-prepared samples the coordination changes are predominantly for Ni2+ ions and that the air-annealed samples contain both Fe3+/Fe4+ and Ni2+/Ni3+ ions.
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| 6. |
- Rahman, Seikh M. H., et al.
(författare)
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Proton conductivity of hexagonal and cubic BaTi1-XScxO3-delta (0.1 <= x <= 0.8)
- 2014
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 43:40, s. 15055-15064
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Tidskriftsartikel (refereegranskat)abstract
- BaTi1-xScxO3-delta (X = 0.1-0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti4+ for Sc3+ gives a hexagonal perovskite structure, whereas high substitution (x = 0.5-0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H(2)0 and D2O, conditions for BaTi1-xScXO3-delta,(x = 0.2, 0.6 and 0.7). In the temperature range of 150-600 C-circle, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8,Sc0.2O3-delta is approx. two orders of magnitude lower than that of the more heavily substituted cubic phases. Conductivity is also found to be higher in dry O-2 than in Ar in the whole temperature range of 150-1000 C-circle, characteristic of a significant contribution from p-type charge carriers under oxidising atmospheres. Greater Sc3+ substitution leads to a higher proton concentration and the highest proton conductivity (sigma similar to 2 x 10(-3) S cm(-1) at 600 degrees C) is found for the BaTi(0.3)Sc(07)cO(3-delta) composition.
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| 7. |
- Samain, Louise, et al.
(författare)
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Crystal structure and high-temperature properties of the Ruddlesden-Popper phases Sr3-xYx(Fe1.25Ni0.75)O7-delta (0 <= x <= 0.75)
- 2015
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 227, s. 45-54
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Tidskriftsartikel (refereegranskat)abstract
- Ruddlesden-Popper n=2 member phases Sr3-xYxFe1.25Ni0.75O7-delta, 0 <= x <= 0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mossbauer spectroscopy. Both samples as-prepared at 1300 degrees C under N-2(g) flow and samples subsequently air-annealed at 900 degrees C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with delta=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mossbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a delta value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mossbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K-1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.
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