| 1. |
- Ali, Sharafat, 1976-, et al.
(författare)
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A cubic calcium oxynitrido-silicate, Ca2.89Si2N1.76O4.24
- 2011
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Ingår i: Acta Crystallographica Section E. - 1600-5368. ; 67
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, tricalcium oxynitride silicate, withcomposition Ca3-xSi2N2-2xO4+2x (x ’ 0.12), is a perovskiterelatedcalcium oxynitrido silicate containing isolated oxynitridosilicate 12-rings. The N atoms are statistically disorderedwith O atoms (occupancy ratio N:O = 0.88:0.12) and occupythe bridging positions in the 12 ring oxynitrido silicate anion,while the remaining O atoms are located at the terminalpositions of the Si(O,N)4 tetrahedra. The majority of the Ca2+cations fill the channels along [100] in the packing of the 12-ring anions. The rest of these cations are located at severalpositions, with partial occupancy, in channels along the bodydiagonals.
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| 2. |
- Biendicho, Jordi Jacas, et al.
(författare)
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Synthesis and characterization of perovskite-type SrxY1−xFeO3−δ (0.63≤x<1.0) and Sr0.75Y0.25Fe1−yMyO3−δ (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-d were prepared in air (0.71 ≤ x ≤ 0.91) as well as in N2 (x=0.75 and 0.79) at 1573K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF 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 high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along <100>p with G± ~0.4<100>p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K-1 in air at 298-673K. At 773-1173K TEC increases up to 17.2 ppm K-1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-δ (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 Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79.
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Cai, Yanbing, et al.
(författare)
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Sialon Ceramics Prepared by Using CaH2 as a Sintering Additive
- 2008
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Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 91:9, s. 2997-3004
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Tidskriftsartikel (refereegranskat)abstract
- In developing elongated a-sialon grains, a nitrogen-rich liquidphase sintering method was introduced by using CaH2 as asintering aid, so as to vary the N/O ratio of the liquid phaseformed in the sintering process while keeping the Si/Al ratiosconstant. With increasing addition the phase contents changedfrom single b-sialon to dual b/a-sialons and to single Ca-a-sialon.At low N/O ratios the microstructures contained mainlyequiaxed b-sialon grains, and at high N/O ratios well facetedelongated Ca-a-sialon grains. The improved toughness(KIC57.8 MPa .m1/2) and hardness (HV10517.5 GPa) propertiescan be attributed to the formation of interlocked microstructures.High-temperature compressive deformation testsindicated that the deformation onset temperature is determinedmainly by the Si/Al and N/O ratios, whereas the deformationrate is affected by the microstructure, i.e., the morphology andamounts of elongated a-sialon grains and residual glass phase,especially for the sialons with low N/O ratios.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Cai, Yanbing, et al.
(författare)
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Thermal Properties of Nitrogen-Rich Ca-α-Sialons
- 2009
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 29:16, s. 3409-3417
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen-rich Ca-α-Sialon (CaxSi12−2xAl2xN16 with x = 0.2, 0.4, and 0.8, 1.2 and 1.6) ceramics were prepared from the mixtures of Si3N4, AlN and CaH2 powders in a hot press at 1800 °C using a pressure of 35 MPa and a holding time of 4 h, and then were investigated with respect to reaction mechanism, phase stability and oxidation resistance. In addition the sample with x = 1.6 was prepared in the temperature range 600–1800 °C using a pressure of 35 MPa and a holding time of 2 h. The α-Sialon phase was first observed at 1400 °C but the α-Si3N4 and AlN phases were still present at 1700 °C. Phase pure Ca-α-Sialon ceramics could not be obtained until the sintering temperature reached 1800 °C. The phase pure nitrogen-rich Ca-α-Sialon exhibited no phase transformation in the temperature range 1400–1600 °C. In general, mixed α/β-Sialon showed better oxidation resistance than pure α-Sialon in the low temperature range (1250–1325 °C), while α-Sialons with compositions located at α/β-Sialon border-line showed significant weight gains over the entire temperature range tested (1250–1400 °C). The phases formed upon oxidation were characterized by X-ray, SEM and TEM studies.
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| 12. |
- Chamoun, Mylad, 1989-
(författare)
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Rechargeable Aqueous Batteries Based on Available Resources : Investigation and Development towards Efficient Battery Performance
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Batteries employing water based electrolytes enable extremely low manufacturing costs and are inherently safer than Li-ion batteries. Batteries based on zinc, manganese dioxide, iron, and air have high energy relevancy, are not resource restricted, and can contribute to large scale energy storage solutions. Zinc has a rich history as electrode material for primary alkaline Zn–MnO2 batteries. Historically, its use in secondary batteries has been limited because of morphological uncertainties and passivation effects that may lead to cell failure. Manganese dioxide electrodes are ineffective as rechargeable electrodes because of failure mechanisms associated with phase transformations during cycling. The irreversibility of manganese dioxide is strongly correlated to the formation of the electrochemically inactive spinel, Mn3O4/ZnMn2O4. The development of the iron electrode for Fe–air batteries was initiated in late the 1960s and these batteries still suffer from charging inefficiency, due to the unwanted hydrogen evolution reaction. Meanwhile, the air electrode is limited in long-term operation because of the sluggish oxygen evolution and reduction kinetics. These limitations of the Fe–air battery yield poor overall efficiencies, which bring vast energy losses upon cycling.Herein, the limitations described above were countered for rechargeable Zn–MnO2 and Fe–air batteries by synthesizing electrode materials and modifying electrolyte compositions. The electrolyte mixture of 1 M KOH + 3 M LiOH for rechargeable alkaline Zn–MnO2 batteries limited the formation of the inactive spinels and improved their cycle life significantly. Further, the formation of the inactive spinels was overcome in mildly acidic electrolytes containing 2 M ZnSO4, enabling the cells to cycle reversibly at lower pH via a distinctive reaction mechanism. The iron electrodes were improved with the addition of stannate, which suppressed hydrogen evolution. Furthermore, optimal charge protocols of the iron electrodes were identified to minimize the hydrogen evolution rate. On the air electrode, the synthesized NiCo2O4 showed excellent bifunctional catalytic activity for oxygen evolution and reduction, and was incorporated to a flow assisted rechargeable Fe–air battery, in order to prove the practicability of this technology. Studies of the electrode materials on the micro, macro, nano, and atomic scales were carried out to increase the understanding of the nature of and interactions between of these materials. This included both in operando and ex situ characterization. X-ray and neutron radiation, and analytical- and electrochemical methods provided insight to improve the performance and cycle life of the batteries.
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| 13. |
- Chernov, S. V., et al.
(författare)
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Sr2GaScO5, Sr10Ga6Sc4O25, and SrGa0,75Sc0,25O2,5: a Play in the Octahedra to Tetrahedra Ratio in Oxygen-Deficient Perovskites
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:2, s. 1094-1103
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Tidskriftsartikel (refereegranskat)abstract
- Three different perovskite-related phases were isolated in the SrGa(1-x)Sc(x)O(2.5) system: Sr(2)GaScO(5), Sr(10)Ga(6)Sc(4)O(25), and SrGa(0.75)Sc(0.25)O(2.5), Sr(2)GaScO(5) (x = 0.5) crystallizes in a brownrnillerite-type structure [space group (S.G.) Icmm, a = 5.91048(5) angstrom, b = 15.1594(1) angstrom, and c = 5.70926(4) angstrom] with complete ordering of Sc(3+) and Ga(3+) over octahedral and tetrahedral positions, respectively. The crystal structure of Sr(10)Ga(6)Sc(4)O(25) (x = 0.4) was determined by the Monte Carlo method and refined using a combination of X-ray, neutron, and electron diffraction data [S.G. I4(1)/a, a = 17.517(1) angstrom, c = 32.830(3) angstrom]. It represents a novel type of ordering of the B cations and oxygen vacancies in perovskites. The crystal structure of Sr(10)Ga(6)Sc(4)O(25) can be described as a stacking of eight perovskite layers along the c axis ...[-(Sc/Ga)O(1.6)-SrO(0.8)-(Sc/Ga)O(1.8)-SrO(0.8)-](2 center dot center dot center dot) Similar to Sr(2)GaScO(5), this structure features a complete ordering of the Sc(3+) and Ga(3+) cations over octahedral and tetrahedral positions, respectively, within each layer. A specific feature of the crystal structure of Sr(10)Ga(6)Sc(4)O(25) is that one-third of the tetrahedra have one vertex not connected with other Sc/Ga cations. Further partial replacement of Sc(3+) by Ga(3+) leads to the formation of the cubic perovskite phase SrGa(0.75)Sc(0.25)O(2.5) (x = 0.25) with a = 3.9817(4) angstrom. This compound incorporates water molecules in the structure forming SrGa(0.75)Sc(0.25)O(2.5)center dot xH(2)O hydrate, which exhibits a proton conductivity of similar to 2.0 x 10(-6) S/cm at 673 K.
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| 14. |
- Christensen, Kirsten E., et al.
(författare)
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An open-framework silicogermanate with 26-ring channels built from seven-coordinated (Ge,Si)10(O, OH)28 clusters
- 2008
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:12, s. 3758-3759
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Tidskriftsartikel (refereegranskat)abstract
- We report a new open-framework silicogermanate SU-61 containing 26-ring channels with a low framework density. It can be seen as a crystalline analogue to the mesoporous silica MCM-41. The structure is built from the assembly of (Ge,Si)10(O,OH)28 clusters. It is the first time that silicon has been successfully introduced in the Ge10 cluster in significant amounts (21% of the tetrahedral sites). Five- and six-coordinated Ge10 clusters have previously been observed in other germanate compounds leading to either dense or open structures. In SU-61, the seven-coordinated clusters fall onto yet another underlying net, the osf net. SU-61, along with other Ge10 based frameworks, shows the versatility of the germanate system to adopt defined topologies playing on the connectivity of the clusters following the principles of net decoration and scale chemistry.
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| 15. |
- De Sloovere, Dries, et al.
(författare)
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Phase Engineering via Aluminum Doping Enhances the Electrochemical Stability of Lithium-Rich Cobalt-Free Layered Oxides for Lithium-Ion Batteries
- 2024
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Ingår i: Small. - 1613-6810 .- 1613-6829. ; 20:31, s. 2400876-
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Tidskriftsartikel (refereegranskat)abstract
- Lithium-rich, cobalt-free oxides are promising potential positive electrode materials for lithium-ion batteries because of their high energy density, lower cost, and reduced environmental and ethical concerns. However, their commercial breakthrough is hindered because of their subpar electrochemical stability. This work studies the effect of aluminum doping on Li1.26Ni0.15Mn0.61O2 as a lithium-rich, cobalt-free layered oxide. Al doping suppresses voltage fade and improves the capacity retention from 46% for Li1.26Ni0.15Mn0.61O2 to 67% for Li1.26Ni0.15Mn0.56Al0.05O2 after 250 cycles at 0.2 C. The undoped material has a monoclinic Li2MnO3-type structure with spinel on the particle edges. In contrast, Al-doped materials (Li1.26Ni0.15Mn0.61-xAlxO2) consist of a more stable rhombohedral phase at the particle edges, with a monoclinic phase core. For this core-shell structure, the formation of Mn3+ is suppressed along with the material's decomposition to a disordered spinel, and the amount of the rhombohedral phase content increases during galvanostatic cycling. Whereas previous studies generally provided qualitative insight into the degradation mechanisms during electrochemical cycling, this work provides quantitative information on the stabilizing effect of the rhombohedral shell in the doped sample. As such, this study provides fundamental insight into the mechanisms through which Al doping increases the electrochemical stability of lithium-rich cobalt-free layered oxides.
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| 16. |
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| 17. |
- Eden, Mattias, et al.
(författare)
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Al and O substitutions in BaS-phases, Ba2AlxSi12-xN16-xO2+x : A TEM, XRD and solid-state NMR study
- 2008
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Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 10:1, s. 50-60
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Tidskriftsartikel (refereegranskat)abstract
- In a series of Ba-based oxonitrido-silicate S-phases (Ba2AlxSi12-xN16-xO2+x) spanning a compositional range up to x approximate to 3, we examine the incorporation of Al and O by Si-29 and Al-27 magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) and Al-27 triple-quantum MAS (3QMAS). The 3QMAS spectra reveal Al-27 signals from two distinct structural environments, assigned to AlN4 or AlN3O tetrahedra, respectively, and with their relative amounts depending on the S-phase substitution parameter x. Si-29 NMR show variable fractions of SiN4 and SiN3O environments. The NMR results accord overall with a structural substitution model for which O enters at one crystallographic position (occupied according to N4-xOx), in conjunction with a random Al for Si substitution at two distinct crystallographic positions. This leads to S-phase frameworks built from SiN4, SiN3O, AlN4 and AlN3O tetrahedra.
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| 18. |
- Eklof, Daniel, et al.
(författare)
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Mysterious SiB3: Identifying the Relation between alpha- and beta-SiB3
- 2019
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Ingår i: ACS Omega. - : AMER CHEMICAL SOC. - 2470-1343. ; 4:20, s. 18741-18759
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Tidskriftsartikel (refereegranskat)abstract
- Binary silicon boride SiB3 has been reported to occur in two forms, as disordered and nonstoichiometric alpha-SiB3-x, which relates to the alpha-rhombohedral phase of boron, and as strictly ordered and stoichiometric beta-SiB3. Similar to other boron-rich icosahedral solids, these SiB3 phases represent potentially interesting refractory materials. However, their thermal stability, formation conditions, and thermodynamic relation are poorly understood. Here, we map the formation conditions of alpha-SiB3-x and beta-SiB3 and analyze their relative thermodynamic stabilities. alpha-SiB3-x is metastable (with respect to beta-SiB3 and Si), and its formation is kinetically driven. Pure polycrystalline bulk samples may be obtained within hours when heating stoichiometric mixtures of elemental silicon and boron at temperatures 1200-1300 degrees C. At the same time, alpha-SiB3-x decomposes into SiB6 and Si, and optimum time-temperature synthesis conditions represent a trade-off between rates of formation and decomposition. The formation of stable beta-SiB3 was observed after prolonged treatment (days to weeks) of elemental mixtures with ratios Si/B = 1:11:4 at temperatures 1175-1200 degrees C. The application of high pressures greatly improves the kinetics of SiB3 formation and allows decoupling of SiB3 formation from decomposition. Quantitative formation of beta-SiB3 was seen at 1100 degrees C for samples pressurized to 5.5-8 GPa. beta-SiB3 decomposes peritectoidally at temperatures between 1250 and 1300 degrees C. The highly ordered nature of beta-SiB3 is reflected in its Raman spectrum, which features narrow and distinct lines. In contrast, the Raman spectrum of alpha-SiB3-x is characterized by broad bands, which show a clear relation to the vibrational modes of isostructural, ordered B6P. The detailed composition and structural properties of disordered alpha-SiB3-x were ascertained by a combination of single-crystal X-ray diffraction and Si-29 magic angle spinning NMR experiments. Notably, the compositions of polycrystalline bulk samples (obtained at T amp;lt;= 1200 degrees C) and single crystal samples (obtained from Si-rich molten Si-B mixtures at T amp;gt; 1400 degrees C) are different, SiB2.93(7) and SiB2.64(2), respectively. The incorporation of Si in the polar position of B-12 icosahedra results in highly strained cluster units. This disorder feature was accounted for in the refined crystal structure model by splitting the polar position into three sites. The electron-precise composition of alpha-SiB3-x is SiB2.5 and corresponds to the incorporation of, on average, two Si atoms in each B-12 icosahedron. Accordingly, alpha-SiB3-x constitutes a mixture of B10Si2 and B11Si clusters. The structural and phase stability of alpha-SiB3-x were explored using a first-principles cluster expansion. The most stable composition at 0 K is SiB2.5, which however is unstable with respect to the decomposition beta-SiB3 + Si. Modeling of the configurational and vibrational entropies suggests that alpha-SiB3-x only becomes more stable than beta-SiB3 at temperatures above its decomposition into SiB6 and Si. Hence, we conclude that alpha-SiB3-x is metastable at all temperatures. Density functional theory electronic structure calculations yield band gaps of similar size for electron-precise alpha-SiB2.5 and beta-SiB3, whereas alpha-SiB3 represents a p-type conductor.
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| 19. |
- Eklöf, Daniel, et al.
(författare)
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Mysterious SiB3 : Identifying the Relation between α- and β-SiB3
- 2019
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:20, s. 18741-18759
-
Tidskriftsartikel (refereegranskat)abstract
- Binary silicon boride SiB3 has been reported to occur in two forms, as disordered and nonstoichiometric alpha-SiB3-x, which relates to the alpha-rhombohedral phase of boron, and as strictly ordered and stoichiometric beta-SiB3. Similar to other boron-rich icosahedral solids, these SiB3 phases represent potentially interesting refractory materials. However, their thermal stability, formation conditions, and thermodynamic relation are poorly understood. Here, we map the formation conditions of alpha-SiB3-x and beta-SiB3 and analyze their relative thermodynamic stabilities. alpha-SiB3-x is metastable (with respect to beta-SiB3 and Si), and its formation is kinetically driven. Pure polycrystalline bulk samples may be obtained within hours when heating stoichiometric mixtures of elemental silicon and boron at temperatures 1200-1300 degrees C. At the same time, alpha-SiB3-x decomposes into SiB6 and Si, and optimum time-temperature synthesis conditions represent a trade-off between rates of formation and decomposition. The formation of stable beta-SiB3 was observed after prolonged treatment (days to weeks) of elemental mixtures with ratios Si/B = 1:11:4 at temperatures 1175-1200 degrees C. The application of high pressures greatly improves the kinetics of SiB3 formation and allows decoupling of SiB3 formation from decomposition. Quantitative formation of beta-SiB3 was seen at 1100 degrees C for samples pressurized to 5.5-8 GPa. beta-SiB3 decomposes peritectoidally at temperatures between 1250 and 1300 degrees C. The highly ordered nature of beta-SiB3 is reflected in its Raman spectrum, which features narrow and distinct lines. In contrast, the Raman spectrum of alpha-SiB3-x is characterized by broad bands, which show a clear relation to the vibrational modes of isostructural, ordered B6P. The detailed composition and structural properties of disordered alpha-SiB3-x were ascertained by a combination of single-crystal X-ray diffraction and Si-29 magic angle spinning NMR experiments. Notably, the compositions of polycrystalline bulk samples (obtained at T <= 1200 degrees C) and single crystal samples (obtained from Si-rich molten Si-B mixtures at T > 1400 degrees C) are different, SiB2.93(7) and SiB2.64(2), respectively. The incorporation of Si in the polar position of B-12 icosahedra results in highly strained cluster units. This disorder feature was accounted for in the refined crystal structure model by splitting the polar position into three sites. The electron-precise composition of alpha-SiB3-x is SiB2.5 and corresponds to the incorporation of, on average, two Si atoms in each B-12 icosahedron. Accordingly, alpha-SiB3-x constitutes a mixture of B10Si2 and B11Si clusters. The structural and phase stability of alpha-SiB3-x were explored using a first-principles cluster expansion. The most stable composition at 0 K is SiB2.5, which however is unstable with respect to the decomposition beta-SiB3 + Si. Modeling of the configurational and vibrational entropies suggests that alpha-SiB3-x only becomes more stable than beta-SiB3 at temperatures above its decomposition into SiB6 and Si. Hence, we conclude that alpha-SiB3-x is metastable at all temperatures. Density functional theory electronic structure calculations yield band gaps of similar size for electron-precise alpha-SiB2.5 and beta-SiB3, whereas alpha-SiB3 represents a p-type conductor.
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| 20. |
- Eklöf, Daniel, et al.
(författare)
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Transport Properties of Ag-doped ZnSb
- 2021
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Ingår i: Zeitschrift für Anorganische und Allgemeines Chemie. - : Wiley. - 0044-2313 .- 1521-3749. ; 647:2-3, s. 34-40
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Tidskriftsartikel (refereegranskat)abstract
- The intermetallic compound ZnSb is a (II-V) narrow gap semiconductor with interesting thermoelectric properties. Electrical resistivity, Hall coefficient, thermopower and thermal conductivity were measured up to 400 K on Ag-doped samples with concentrations 0.2, 0.5, 1, 2, and 3 at.%, which were consolidated to densities in excess of 99.5 % by spark plasma sintering. The work confirms a huge improvement of the thermoelectric Figure-of-merit, ZT, upon Ag doping. The optimum doping level is near 0.5 at.% Ag and results in ZT values around 1.05 at 390 K. The improvement stems from a largely decreased resistivity, which in turn relates to an increase of the hole charge carrier concentration by two orders of magnitude. It is argued that Ag can replace minute concentrations of Zn (on the order of 0.2 at.%) in the crystal structure which enhances the intrinsic impurity band of ZnSb. Excess Ag was found to segregate in grain boundaries. So the best performing material may be considered as a composite Zn similar to 0.998Ag similar to 0.002Sb/Ag-similar to 0.003.
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| 21. |
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| 22. |
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| 23. |
- 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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| 24. |
- Grins, Jekabs, et al.
(författare)
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Phases in the ZrxTa1-x(O,N)y System, Formed by Ammonolyses of Zr-Ta Gels. Preparation of Baddeleyite Type Solid Solution Phase ZrxTa1-xO1+xN1-x, 0≤x≤1
- 1994
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 4, s. 1293-1301
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Tidskriftsartikel (refereegranskat)abstract
- Phase formation in the system ZrxTa1–x(O,N)y has been studied by ammonolysis of Zr-Ta gels, prepared by the sol–gel technique, at temperatures between 700 and 1000 °C. The starting gels and observed phases were characterised by X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (SEM and TEM) and thermogravimetric (TG) analysis. Oxynitride phases of compositions ZrxTa1–xO1 +xN1–x, 0≤x≤1, with the baddeleyite-type structure, were prepared at 800 °C. The unit-cell volume increased linearly from 127.8 Å3 for TaON (x= 0) to 140.9 Å3 for ZrO2(x= 1). The structure was verified for the composition Zr0.4Ta0.6O1.6N0.4(x= 0.4) by a Rietveld refinement (RF= 3.5%) using Cu-Kα1, XRPD data. An orthorhombic oxynitride phase was observed in preparations at 700 °C for 0.26 ≤x≤ 0.90 in ZrxTa1–xO1+xN1–x. Unit-cell parameters and powder X-ray reflection intensities agree with an orthorhombic ZrO2 type structure. According to X-ray data, a cubic solid solution phase with a fluorite related subcell is present in materials prepared at 900 °C for 0.26≤x≤ 0.68. However, electron microdiffraction patterns suggest a metrically monoclinic unit cell with a = 6.1 Å, b= 14.1 Å, c= 7.1 Å and β= 125°. The Ta3N5, type of structure was found to incorporate up to ca. 18 atom% Zr at 900 and 1000 °C.
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| 25. |
- Grins, Jekabs
(författare)
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Studies on some pyrochlore type solid electrolytes
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This article summarizes ionic conductivity studies on a number of compounds crystallizing in the pyrochlore type structure. The pyrochlore structure is described, and the determination of ionic conductivities by means of impedance measurements is discussed. The results of the characterization of the samples by X-ray measurements and TG analysis are also discussed.
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| 26. |
- Grins, Jekabs, et al.
(författare)
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Synthesis and structural characterisation of MnWN2 prepared by ammonolysis of MnWO4
- 1995
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 5, s. 571-575
-
Tidskriftsartikel (refereegranskat)abstract
- A new ternary transition-metal nitride, the composition of which is close to MnWN2, has been synthesized by ammonolysis of X-ray amorphous MnWO4 at 800 degrees C. The Guinier-Hagg powder pattern could be indexed with a hexagonal cell with a = 2.9213(3) Angstrom and c = 10.957(2) Angstrom. Although no superstructure reflections could be observed in the X-ray powder diffraction pattern, such reflections were revealed by electron diffraction. In most of the crystallites investigated, the relationship between supercell and the hexagonal (sub)cell was found to be a(super) = root 3a(hex). A Rietveld structure determination, based on space group P6(3)me (no. 186), showed that the metal atoms were approximately close-packed in an ABAC... sequence with Mn at site 2(a) and W at site 2(d), The lowest R(F) value (10%) was obtained for an ordered structure model with the Mn and N atoms occupying 2(a) and the W and N at sites 2(b). Measurements of the magnetic susceptibility, and of the electrical resistivity, indicated a metallic behaviour of MnWN2
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| 27. |
- GRINS, Jekabs, et al.
(författare)
-
SYNTHESIS OF OXYNITRIDE PEROVSKITES [AZRXTA1-XO2+XN1-X, A=CA, SR, BA AND 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1]
- 1994
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Ingår i: Materials research bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 29:7, s. 801-809
-
Tidskriftsartikel (refereegranskat)abstract
- Solid solution perovskite phases AZrxTa1-xO2+xN1-x, with A = Ca, Sr, Ba and 0 less-than-or-equal-to x less-than-or-equal-to 1 have been synthesised by ammonolysis of mixtures of Ta-Zr gels and ACO3. The gels were made by the sol-gel technique using TaCl5 and Zr-n-propoxide as precursors. The perovskite phases have been characterised by X-ray powder diffraction and elemental analysis for one composition from each subsystem has been performed. The Ca compounds were found to be orthorhombic for all x. The orthorhombic GdFeO3 type perovskite structure was verified for the composition CaZr0.52Ta0.48O2.52N0.48 by a Rietveld refinement to R(F) = 2.3 %, using CuKalpa1 X-ray powder diffractometer data. According to X-ray powder diffraction data, the Sr compounds are orthorhombic for x greater-than-or-equal-to 0.60 and cubic for lower x values. The Ba compounds were found to be cubic for all x.
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| 28. |
- Grins, Jekabs, et al.
(författare)
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Synthesis, Structure and Magnetic Susceptibility of the Oxynitride Spinel Mn2(MnTa3)N6-δO2+δ, 0 ≤ δ ≤ 1
- 1995
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 117:1, s. 48-54
-
Tidskriftsartikel (refereegranskat)abstract
- The oxynitride spinel Mn-2(MnTa3)N6-deltaO2+delta, with 0 less than or equal to delta less than or equal to 1, has been synthesized at 1175 K by ammonolysis of a mixture of a Ta-containing xerogel and Mn(OAc)(2) . 4H(2)O. The N content was determined by combustion analysis and thermogravimetric oxidation, yielding a composition confined between Mn-2(MnTa3)N6O2 (delta = 0) and Mn-2(MnTa3)N5O3 (delta = 1). The structure is cubic, with space group Fd3m and a = 8.8353(3) Angstrom. It was refined using the Rietveld technique and neutron powder diffraction data collected at room temperature and 15 K, to R(F) = 2.9 and 3.8%, respectively. The tetrahedral sites are occupied only by Mn atoms and the octahedral sites statistically by 25% Mn and 75% Ta atoms. The N and O atoms are randomly distributed over the anion sites. The magnetic susceptibility exhibits a maximum at 29 K and a Curie-Weiss behavior at higher temperatures with theta(a) = -250(20) K and mu(eff) = 5.7(2) Bohr magnetons per Mn atom. The neutron powder diffraction data collected at 15 K showed no evidence of magnetic ordering. A NaCl-type phase with a = 4.4382(2) Angstrom and tentative composition Mn0.8Ta0.2(O,N) was observed in preparations at 1175 K. A hexagonal Mn4Ta2(O,N)(x) phase with cell dimensions a = 5.3024(4) Angstrom, c = 14.493(2) Angstrom was obtained at 973 K. (C) 1995 Academic Press, Inc.
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| 29. |
- Grins, Jekabs, et al.
(författare)
-
Synthesis, structure and magnetic susceptibility of the oxynitride spinell Mn2(MnTa3)N6-δO2+δ, 0≤δ≤1
- 1995
-
Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 117:1, s. 48-54
-
Tidskriftsartikel (refereegranskat)abstract
- The oxynitride spinel Mn2(MnTa3)N6-δO2+δ, with 0 ≤ δ ≤ 1, has been synthesized at 1175 K by ammonolysis of a mixture of a Ta-containing xerogel and Mn(OAc)2 · 4H2O. The N content was determined by combustion analysis and thermogravimetric oxidation, yielding a composition confined between Mn2(MnTa3)N6O2 (δ = 0) and Mn2(MnTa3)N5O3 (δ = 1). The structure is cubic, with space group Fd3m and a = 8.8353(3) Å. It was refined using the Rietveld technique and neutron powder diffraction data collected at room temperature and 15 K, to RF = 2.9 and 3.8%, respectively. The tetrahedral sites are occupied only by Mn atoms and the octahedral sites statistically by 25% Mn and 75% Ta atoms. The N and O atoms are randomly distributed over the anion sites. The magnetic susceptibility exhibits a maximum at 29 K and a Curie-Weiss behavior at higher temperatures with θa = -250(20) K and μeff = 5.7(2) Bohr magnetons per Mn atom. The neutron powder diffraction data collected at 15 K showed no evidence of magnetic ordering. A NaCl-type phase with a = 4.4382(2) Å and tentative composition Mn0.8Ta0.2(O,N) was observed in preparations at 1175 K. A hexagonal Mn4Ta2(O,N)x phase with cell dimensions a = 5.3024(4) Å, c = 14.493(2) Å was obtained at 973 K.
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| 30. |
- Gueguen, Yann, et al.
(författare)
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Viscosity of high-nitrogen content Ca-Si-O-N glasses
- 2010
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 30:16, s. 3455-3458
-
Tidskriftsartikel (refereegranskat)abstract
- The viscosity of three high-nitrogen content Ca-Si-O-N glasses, with 30-58 e/o N and 36-39 e/o Ca, was determined by micro-indentation. The measurements were made using an automated set-up, designed and built in-house, capable of measurements up to 1200 degrees C with applied loads of 0.01-15 N. The viscosity increases significantly with the nitrogen content and reaches viscosity values close to reported values for rare-earth silica oxynitride glasses. The glass transition temperatures range between 878 and 995 degrees C and are in very good agreement with values measured by differential thermal analysis. The apparent viscosity activation energies are very high, ranging from 855 to 2170 kJ/mol. The glasses can accordingly be classified as being both very refractory and very fragile. Implications of the viscosity values and mechanical properties of the glasses for their structures are discussed.
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| 31. |
- Gunawidjaja, Philips N., et al.
(författare)
-
Biomimetic Apatite Mineralization Mechanisms of Mesoporous Bioactive Glasses as Probed by Multinuclear ³¹P, ²⁹Si, ²³Na and ¹³C Solid State NMR
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:45, s. 19345-19356
-
Tidskriftsartikel (refereegranskat)abstract
- An array of magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy experiments is applied to explore the surface reactions of a mesoporous bioactive glass (MBG) of composition Ca0.10Si0.85P0.04O1.90 when subjected to a simulated body fluid (SBF) for variable intervals. Powder X-ray diffraction and 31P NMR techniques are employed to quantitatively monitor the formation of an initially amorphous calcium phosphate surface layer and its subsequent crystallization into hydroxycarbonate apatite (HCA). Prior to the onset of HCA formation, 1H → 29Si cross-polarization (CP) NMR evidence dissolution of calcium ions; a slightly increased connectivity of the speciation of silicate ions is observed at the MBG surface over 1 week of SBF exposure. The incorporation of carbonate and sodium ions into the bioactive orthophosphate surface layer is explored by 1H → 13C CPMAS and 23Na NMR, respectively. We discuss similarities and distinctions in composition−bioactivity relationships established for traditional melt-prepared bioglasses compared to MBGs. The high bioactivity of phosphorus-bearing MBGs is rationalized to stem from an acceleration of their surface reactions due to presence of amorphous calcium orthophosphate clusters of the MBG pore wall.
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| 32. |
- Gunawidjaja, Philips N., et al.
(författare)
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Quantifying apatite formation and cation leaching from mesoporous bioactive glasses in vitro : a SEM, solid-state NMR and powder XRD study
- 2012
-
Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:15, s. 7214-7223
-
Tidskriftsartikel (refereegranskat)abstract
- By employing solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction (PXRD), and scanning electron microscopy coupled with energy-dispersive X-ray (EDX) spectroscopy, we compare the biomimetic growth of calcium hydroxyapatite (HA) from an ordered mesoporous bioactive glass (MBG) in simulated body fluid (SBF) and buffered water solutions. For the latter medium, we also examine the effects of using two different MBG concentrations. We evaluate the predicting powers of PXRD and P-31 NMR for directly quantifying the relative amounts of biomimetic amorphous calcium phosphate (ACP) and HA: we observe a very good agreement between the two analytical techniques. Thanks to their mesoporous channel system, fluids readily penetrate throughout sub-mm sized MBG grains, as evidenced by EDX. The latter revealed distinct element-mappings across the material after its exposure to SBF compared to water. Under our in vitro conditions involving relatively high MBG-loadings in the solutions, the HA formation reduces in SBF relative to buffered water, particularly for increasing MBG concentration. These features stem from a high [Ca2+]/[PO43-] ratio resulting in the fluid medium, which retards the HA crystallization by inducing a rapid ACP precipitation and an accompanying depletion of phosphate ions in the solution. This has bearings on the design of bioactivity comparisons of bioglasses exhibiting significantly different cation compositions.
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| 33. |
- Gustafsson, Mikaela, 1980-, et al.
(författare)
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A family of highly stable lanthanide metal-organic frameworks: structural evolution and catalytic activity
- 2010
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 22:11, s. 3316-3322
-
Tidskriftsartikel (refereegranskat)abstract
- A family of homeotypic porous lanthanide metal−organic frameworks (MOFs), [Ln(btc)(H2O)]·guest (Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Ho (6), Er (7), and Yb (8); guest: DMF or H2O) was synthesized. The structures of the as-synthesized compounds are tetragonal and contain 1D channels with accessible lanthanide ions. In situ single crystal X-ray diffraction shows that 1 undergoes a single-crystal to polycrystalline to single-crystal transformation from room temperature to 180 °C. During the release of DMF and water molecules from the channels by evacuation and subsequent heating, the structures of 1 and 7 transformed from tetragonal to monoclinic, and then to tetragonal, while the structure of 8 remained tetragonal. The transformation between the monoclinic and the low temperature tetragonal phases is reversible. The Ln(btc) MOFs are stable to at least 480 °C and are among the most thermally stable MOFs. The Ln(btc) MOFs act as efficient Lewis acid catalysts for the cyanosilylation of aldehydes yielding cyanohydrins in high yields within short reaction times. 1 also catalyzes the cyanosilylation of less reactive substrates, such as ketones at room temperature. The Ln(btc) MOFs could be recycled and reused without loss of their crystallinity and activity.
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| 34. |
- Gustafsson, Mikaela, et al.
(författare)
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A porous chiral lanthanide metal-organic framework with high thermal stability
- 2008
-
Ingår i: Zeolites and related materials: Trends, targets and challenges. - Amsterdam : Elsevier. - 9780444532978 ; , s. 451-454
-
Konferensbidrag (refereegranskat)abstract
- A metal-organic framework Nd(BTC)(H2O)·DMF (1), which is isostructural with reported Dy(BTC)(H2O)·DMF [1], Tb(BTC)(H2O)1.5·(DMF) (MOF-76) [2] and Eu(BTC)(H2O)·1.5H2O [3], is synthesized. The compound 1 was characterized by SEM/EDS, TGA and in situ PXRD. The structure was determined by single crystal X-ray diffraction. Compound 1 crystallizes in a chiral space group P43, with a = 10.4278(4) and c = 14.2602(12) Å. The structure contains 1D chiral -Nd-O-C-O-Nd- chains linked by the phenyl groups of BTC ligands. The 3D framework contains circular channels along the [001] direction and is stable up to 400°C.
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| 35. |
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| 36. |
- Hakeem, Abbas Saeed, 1970-
(författare)
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Novel Route of Oxynitride Glass Synthesis and Characterisation of Glasses in the Ln-Si-O-N and Ln-Si-Al-O-N Systems
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work has been primarily focused on the glass forming region in the La-Si-O-N system, and attempts have been made to find glass forming regions by adopting a new synthesis route to produce glasses in oxynitride system. This goal can be attained by adding a network modifier in its metallic form instead of as an oxide. In this kind of synthesis, the metallic modifier reacts with nitrogen, which gives a strongly exothermic reaction at particular temperature. The resulting sudden increase in the temperature of the system enables the mixture to react with other components at an early stage of the synthesis. This also provides a high degree of mixing in the melt, and results in larger glass forming regions than reported until now (Figure A shows La from 30 to 62 e/o and nitrogen from 9 of 68 e/o in the La-Si-O-N system). The better property values (Tg-Tc, hardness and refractive index) were achieved over the whole compositional range in the systems.Similarly, glasses containing Al were prepared in the Ln-Si-Al-O-N system, where Ln = La, Sm, Gd, Ho, Dy, and in the Ln-Si-O-N system, with Ln = Pr, Sm, Gd, Dy. Both systems were examined to study the properties at various nitrogen contents, which can be as high as 70 e/o. Glasses were prepared from one particular glass composition in the Pr-Si-O-N system by replacing Pr with various other La components, in order to study the effect of lanthanide substitution on the properties.Figure A. The solid line encloses the glass forming region in the La-Si-O-N system, as determined in the present work. The dotted line represent the glass forming region according to the literature; details are given in figure 11.A new synthesis route has extended the glass forming region, allowing a detailed study of properties such as hardness, glass transition temperature (Tg), glass crystallization temperature (Tc), density and refractive index. Comprehensive studies of properties may give better understanding of the glass structure. The glass transition temperatures range from 950 to 1100°C, and crystallization temperatures from 1050 to 1250°C; the hardness can be as high as 12 GPa and the refractive index attains the value 2.3 in the La-Si-O-N system. Hardness and refractive index were measured in both glass systems (Ln-Si-O-N and Ln-Si-Al-O-N) when substituting cations, and a detailed study of replacing La with Pr in the La-Si-O-N system yielded substantial effects on the properties of the glasses.Higher values of hardness were found: ~13 GPa when applying load of one kg, and an increase with decreasing cation radius was noted in both the Ln-Si-O-N and the Ln-Si-Al-O-N system, containing of 63 and 61 e/o nitrogen, respectively. The hardness increases as the lanthanide ionic radius decreases, and becomes as high as 13.5 GPa in the Dy-Si-O-N system, and the refractive index is 2.3 in the La-Si-O-N system. A linear increase in the properties Tg-Tc, hardness and refractive index with increasing Pr content was found in the Pr-(La)-Si-O-N system.
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| 37. |
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| 38. |
- Heintz, Mads C., et al.
(författare)
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Photovoltaic Wafering Silicon Kerf Loss as Raw Material : Example of Negative Electrode for Lithium‐Ion Battery
- 2023
-
Ingår i: ChemElectroChem. - : Wiley-VCH Verlagsgesellschaft. - 2196-0216. ; 10:19
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon powder kerf loss from diamond wire sawing in the photovoltaic wafering industry is a highly appealing source material for use in lithium-ion battery negative electrodes. Here, it is demonstrated for the first time that the kerf particles from three independent sources contain ~50 % amorphous silicon. The crystalline phase is in the shape of nano-scale crystalline inclusions in an amorphous matrix. From literature on wafering technology looking at wafer quality, the origin and mechanisms responsible for the amorphous content in the kerf loss powder are explained. In order to better understand for which applications the material could be a valuable raw material, the amorphicity and other relevant features are thoroughly investigated by a large amount of experimental methods. Furthermore, the kerf powder was crystallized and compared to the partly amorphous sample by operando X-ray powder diffraction experiments during battery cycling, demonstrating that the powders are relevant for further investigation and development for battery applications.
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| 39. |
- Hu, Jianfeng, 1979-
(författare)
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Grain growth by Ordered Coalescence of crystallites in Ceramics : Grain Growth Mechanisms, Microstructure Evolution and Sintering
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Grain growth and densification process play the two most crucial roles on the microstructure evolution and the achieved performances during sintering of ceramics. In this thesis, the grain growth of SrTiO3, BaTiO3-SrTiO3 solid solutions and Si3N4 ceramics during spark plasma sintering (SPS) were investigated by electron microscopy.SrTiO3 ceramics starting from nanopowders were fabricated by SPS. A novel grain growth mechanism was discovered and named as ordered coalescence (OC) of nanocrystals. This mechanism involved nanocrystals as building blocks and is distinguished from atomic layer epitaxial growth (AEG) in classical sintering theory. The results also revealed that the dominant grain growth mechanism can be changed by varying heating rates. Low rate (10°C/min) gives AEG, whereas high rates (≥ 50°C/min) yields three-dimensional coalescence of nanocrystals, i.e. OC.BaTiO3-SrTiO3 sintered bodies were made by SPS of BaTiO3 and SrTiO3 nanopowders mixtures. A novel Sr1-xBaxTiO3 “solid solution” with mosaic-like single crystal structure was manufactured by OC of the precursor crystallites. This reveals a new path for preparation of solid solution grains or composites. Si3N4 ceramics were prepared from α- or β-Si3N4 nanopowders at the same SPS conditions. The anisotropic OC of precipitated β-Si3N4 crystallites gives elongated β-Si3N4 grains at 1650°C using α-Si3N4 nanopowder. In contrast, AEG leads to the equi-axed β-Si3N4 grains using β-Si3N4 nanopowder. The metastable α- to β-Si3N4 phase transformation and OC accelerates anisotropic grain growth.Grain motions contribute to the densification process during pressureless sintered 3Y-ZrO2 (>87%TD) or SPS of SrTiO3 (>92%TD) ceramics. This extends the sintering range for active grain re-arrangement over that predicted by classical theory.In this thesis a new grain growth mechanism (OC) is proved by using SPS and nanopowders. By OC the microstructural evolution can be manipulated.
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| 40. |
- Iftekhar, ANM Shahriar, 1975-
(författare)
-
Structure-Property-Composition Correlations in Rare-Earth Alumino-silicate Glasses
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rare earth (RE) alumino-silicate (AS) glasses exhibit favorable physical, mechanical and optical properties, such as high values of the glass transition temperature, Vickers hardness, and refractive index. RE2O3-Al2O3-SiO2 glasses have found several industrial applications, for example as components of optical amplifiers and lasers. Many of these features stem from the high cation field-strength (CFS) of the trivalent RE ions (proportional to the valence of the ion divided by the square of its radius), which affects not only the physical properties of the glass, but also their structures.This thesis deals with investigations of four different RE2O3-Al2O3-SiO2 systems, where RE represents either of La, Y, Lu or Sc. The glass forming regions of the latter two were reported by us for the first time. Within each system, glasses were prepared for variable RE, Si and Al contents.The glass structures were investigated by solid-state 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy that informs about the local Si and Al environments in the glass network, which is built from interlinked SiO4 and AlO4 groups. Higher Al coordination numbers were also revealed by 27Al NMR: their amounts were observed to increase markedly as the CFS of the RE ion increases, i.e., along the series La3+ CFS increased.
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| 41. |
- Iftekhar, Shahriar, et al.
(författare)
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Composition–property relationships of the La2O3–Al2O3–SiO2 glass system
- 2010
-
Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 356:20-22, s. 1043-1048
-
Tidskriftsartikel (refereegranskat)abstract
- We report physical properties of density, glass transition temperature, Vickers hardness and refractive index for 15 La–Al–Si–O glasses within the compositional region 10–28 mol% La2O3, 11–30% Al2O3 and 45–78% SiO2. The glass transition temperature varies only slightly between 871 and 883 °C. Both the density (3.25–4.33 g cm−3) and refractive index (1.59–1.70) display similar compositional dependencies and are primarily dictated by the La2O3 content. The hardness (6.4–9.0 GPa) increases with decreasing SiO2 content and to a minor extent also with the amount of La2O3 of the glass. The physical properties, in particular the hardness, are discussed with reference to glass structure. The similarity in the observed properties between the present oxide-based glasses and those of analogous rare-earth (RE) element-containing RE–Si–(Al)–O–N oxynitride glasses is highlighted and discussed in relation to the apparent, but hitherto largely neglected, role of RE-ions to primarily control many enhanced physical properties of oxynitride glasses.
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| 42. |
- Iftekhar, Shahriar, et al.
(författare)
-
Glass Formation and Structure–Property–Composition Relations of theRE2O3–Al2O3–SiO2 (RE = La, Y, Lu, Sc) Systems
- 2011
-
Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 94:8, s. 2429-2435
-
Tidskriftsartikel (refereegranskat)abstract
- We report the glass-forming regions of the ternary Lu2O3–Al2O3–SiO2 and Sc2O3–Al2O3–SiO2 systems. The density, molarvolume, compactness, Vickers hardness, refractive index, aswell as the glass transition (Tg) and crystallization temperatureare compared for two series of RE–Al–Si–O (RE=La, Y, Lu,Sc) glasses that display a constant molar ratio nAl/nSi=1.00,whereas nRE/nSi is equal to either 0.62 or 0.94. Several glassproperties scale roughly linearly with the cation field strength(CFS) of the rare-earth (RE3+) ion, except for the Tg values ofthe Sc-bearing glasses that are significantly lower than expected.Magic-angle spinning 29Si and 27Al nuclear magneticresonance (NMR) reveal enhanced network disorder and increasedrelative populations of AlO5 and AlO6 polyhedra in thealuminosilicate glasses for increasing RE3+ CFS, but overallsimilar Si and Al local environments (chemical shifts and quadrupolarcouplings) in all samples associated with a constant nRE/nSi ratio, except for unexpectedly shielded 29Si NMR signalsobserved from the Sc–Al–Si–O glasses.
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| 43. |
- Iftekhar, Shahriar, et al.
(författare)
-
Phase formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures
- 2008
-
Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 28:4, s. 747-756
-
Tidskriftsartikel (refereegranskat)abstract
- Calcium aluminate is the main constituent in calcium aluminate cements, used in a wide range of applications in construction and mining industries and recently also as biomedical implant. In applications that demand very precise reaction features, such as the biomedical ones, the phase purity is of very high importance. In this paper the formation of CaAl2O4 from CaCO3–Al2O3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 °C. Phase formation was studied in samples both quenched from the holding temperatures and in samples slowly cooled. Samples were characterized by X-ray powder diffraction (XRPD), using Guinier-Hägg film data and the Rietveld method, and scanning (SEM) and transmission (TEM) electron microscopy. Samples for TEM with very high site accuracy were produced using focused ion beam microscopy. In addition to CA (CaAl2O4) the samples contained major amounts of CA2 (CaAl4O7), C12A7 (Ca12Al14O33) and minor amounts of un-reacted A (Al2O3). Trace amounts of C3A (Ca3Al2O6) were observed only for samples heated to 1500 °C. The amount of the Ca-rich phase C12A7 was found to decrease with time as it reacts with A and, to a less degree, CA2 to form CA. In agreement with previous studies the amount of CA2 formed decreases comparatively slowly with time. Its un-reactivity is due to that it is concentrated in isolated porous regions of sizes up to 100 μm. The formation of the Ca aluminates is found to be in response to local equilibriums within small inhomogeneous regions, with no specific phase acting as an intermediate phase. Samples quenched from 1500 °C were found to contain smaller amounts of poorly crystallized phases. A reaction between C and A takes place already at 900 °C, forming a meta-stable orthorhombic modification of CA. The orthorhombic unit cell with a = 8.732(2) Å, b = 8.078(2) Å, c = √3·a = 15.124(4) Å was verified by electron diffraction, revealing frequent twinning and disorder of the crystallites.
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| 44. |
- Iftekhar, Shahriar, et al.
(författare)
-
Properties and Structures of RE2O3-Al2O3-SiO2 (RE=Y, Lu) Glasses Probed by Molecular Dynamics Simulations and Solid-State NMR : The Roles of Aluminum and Rare-Earth Ions for Dictating the Microhardness
- 2012
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:34, s. 18394-18406
-
Tidskriftsartikel (refereegranskat)abstract
- By combining molecular dynamics (MD) simulations with Si-29 and Al-27 magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we present a comprehensive structural report on rare-earth (RE) aluminosilicate (AS) glasses of the RE2O3-Al2O3-SiO2 (RE = Y, Lu) systems, where the latter is studied for the first time. The structural variations stemming from changes in the glass composition within each RE system as well as the effects of the increased cation field-strength (CFS) of Lu3+ relative to Y3+-are explored and correlated to measured physical properties, such as density, molar volume, glass transition temperature, and Vickers hardness (H-V). Si-29 NMR reveals a pronounced network ordering for an increase in either the RE or Al content of the glass. Al mainly assumes tetrahedral coordination, but significant AlO5 and AlO6 populations are present in all structures, with elevated amounts in the Lu-bearing glasses compared to their Y analogues. The MD-derived oxygen speciation comprises up to 3% of free O2- ions, as well as non-negligible amounts (4-19%) of O-[3] coordinations (oxygen triclusters). While the SiO4 groups mainly accommodate the nonbridging oxygen ions, a significant fraction thereof is located at the AlO4 tetrahedra, in contrast to the scenario of analogous alkali- and alkaline-earth metal-based AS glasses. The average coordination numbers (CNs) of Al and RE progressively increase for decreasing Si content of the glass, with the average CN of the RE3+ ions depending linearly on both the amount of Si and the fraction of AlO5 groups in the structure. The Vickers hardness correlates strongly with the average CN of Al, in turn dictated by the CFS and content of the RE3+ ions. This is to our knowledge the first structural rationalization of the well-known compositional dependence of H-V in RE bearing AS glasses.
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| 45. |
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| 46. |
- Keshavarz, Samara, et al.
(författare)
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Magnetic properties of Ruddlesden-Popper phases Sr 3 − x Y x ( Fe 1.25 Ni 0.75 ) O 7 − δ : A combined experimental and theoretical investigation
- 2018
-
Ingår i: Physical Review Materials. - 2475-9953. ; 2:4
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.
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| 47. |
- Keshavarz, Samara, et al.
(författare)
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Magnetic properties of Ruddlesden-Popper phases Sr3−x Yx (Fe1.25 Ni0.75) O7−δ : A combined experimental and theoretical investigation
- 2018
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 2:4
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.
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| 48. |
- Kranak, Verina F., et al.
(författare)
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Hydrogenous Zintl Phase Ba3Si4Hx (x=1-2) : Transforming Si-4 Butterfly Anions into Tetrahedral Moieties
- 2015
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 54:3, s. 756-764
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Tidskriftsartikel (refereegranskat)abstract
- The hydride Ba3Si4Hx (x = 1-2) was prepared by sintering the Zintl phase Ba3Si4, which contains Si-4(6-) butterfly-shaped polyanions, in a hydrogen atmosphere at pressures of 10-20 bar and temperatures of around 300 degrees C. Initial structural analysis using powder neutron and X-ray diffraction data suggested that Ba3Si4Hx adopts the Ba3Ge4C2 type [space group I4/mcm (No. 140), a approximate to 8.44 angstrom, c approximate to 11.95 angstrom, Z = 8] where Ba atoms form a three-dimensional array of corner-condensed octahedra, which are centered by H atoms. Tetrahedron-shaped Si-4 polyanions complete a perovskite-like arrangement. Thus, hydride formation is accompanied by oxidation of the butterfly polyanion, but the model with the composition Ba3Si4H is not charge-balanced. First-principles computations revealed an alternative structural scenario for Ba3Si4Hx, which is based on filling pyramidal Ba-5 interstices in Ba3Si4. The limiting composition is x = 2 [space group P4(2)/mmm (No. 136), a approximate to 8.4066 angstrom, c approximate to 12.9186 angstrom, Z = 8], and for x > 1, Si atoms also adopt tetrahedron-shaped polyanions. Transmission electron microscopy investigations showed that Ba3Si4Hx is heavily disordered in the c direction. Most plausible is to assume that Ba3Si4Hx has a variable H content (x = 1-2) and corresponds to a random intergrowth of P- and I-type structure blocks. In either form, Ba3Si4Hx is classified as an interstitial hydride. Polyanionic hydrides in which H is covalently attached to Si remain elusive.
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| 49. |
- Kravchenko, Ekaterina, et al.
(författare)
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High-temperature characterization of oxygen-eficient K2NiF4-type Nd2-xSrxNiO4-delta O4-delta (x=1.0-1.6) for potential SOFC/SOEC applications
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:47, s. 23852-23863
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Tidskriftsartikel (refereegranskat)abstract
- Previously unexplored oxygen-deficient RuddLesden-Popper Nd2-xSrxNiO4-delta (x = 1.0-1.6) nickelates were evaluated for potential use as oxygen electrode materials for solid oxide fuel and electrolysis ceRs, with emphasis on structural stability, oxygen nonstoichiometry, dimensional changes, and electrical properties. Nd2-xSrxNiO4-delta ceramics possess the K2NiF4-type tetragonal structure under oxidizing conditions at 25-1000 degrees C. Acceptor-type substitution by strontium is compensated by the generation of eLectron-hoLes and oxygen vacancies. Oxygen deficiency increases with temperature and strontium doping reaching -1/8 of oxygen sites for x = 1.6 at 1000 degrees C in air. Strongly anisotropic expansion of the tetragonal Lattice on heating correlated with oxygen nonstoichiometry changes results in an anomalous dilatometric behavior of Nd2-xSrxNiO4-delta ceramics under oxidizing conditions. Moderate thermal expansion coefficients, (11-14) x 10(-6) K-1, ensure however thermomechanical compatibility with common solid electrolytes. Reduction in inert atmosphere induces oxygen vacancy ordering accompanied by a contraction of the Lattice and a decrease of its symmetry to orthorhombic. Nd2-xSrxNiO4-delta ceramics exhibit a p-type metallic-Like electrical conductivity at 500-1000 degrees C under oxidizing conditions, with the highest conductivity (290 S cm(-1) at 900 degrees C in air) observed for x = 1.2. The high Lev& of oxygen deficiency in Sr-rich Nd2-xSrxNiO4 impLies enhanced mixed ionic-electronic transport favorable for electrode applications.
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| 50. |
- Kravchenko, Ekaterina, et al.
(författare)
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High-Temperature Structural and Electrical Characterization of Reduced Oxygen-Deficient Ruddlesden-Popper Nickelates
- 2018
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :28, s. 3320-3329
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature characterization of oxygen-deficient Sr-rich (La1-xSrx)(2)NiO4-delta (x = 0.5-0.8) solid solutions under mildly reducing conditions with p(O-2) approximate to 5x10(-5) atm was performed by employing structural and thermal analysis, TEM, and electrical conductivity measurements. Oxygen losses from the crystal lattice on reduction were found to result in a reversible transition from the tetragonal (I4/mmm) to the orthorhombic (Immm) structure and shrinkage of the crystal lattice for the compositions with x > 0.5. TEM and thermogravimetric analysis evidenced slow kinetics of the structural transition. The increase in oxygen deficiency under reducing conditions is accompanied by localization of the electronic charge carriers, a drop of the p-type electronic conductivity, and a transition from metallic-like to semiconducting behavior. The extent of changes in oxygen nonstoichiometry, unit--cell dimensions, average Ni oxidation state, electron-hole concentration, and electronic conductivity on reduction is interrelated with the strontium content. The results suggest that the electrical conductivity of (La1-xSrx)(2)NiO4-delta ceramics depends mainly on the average Ni oxidation state.
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