| 1. |
- Ahmed, Istaq, 1972, et al.
(författare)
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Effect of co-doping on proton conductivity in perovskite oxides BaZr0.9In0.05M0.05O3−δ (M = Yb3+ or Ga3+)
- 2010
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 35:12, s. 6381-6391
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Tidskriftsartikel (refereegranskat)abstract
- BaZr0.9In0.05M0.05O3-d (M ¼ Ga3+ or Yb3+) has been prepared by solid-statesynthesis route.Rietveld analysis of neutron powder diffraction data on as-prepared samples showed thatboth samples crystallise in the cubic space group Pm-3m. Scanning electron microscopyanalysis showed that the grains intheBaZr0.9In0.05Ga0.05O3-d sample were larger than the BaZr0.9In0.05Yb0.05O3-d sample. Dynamic thermogravimetric analysis indicates that the proton concentration was higher inpre-hydrated BaZr0.9In0.05Ga0.05O3-d sample (40%oftheoretical)than that of BaZr0.9In0.05Yb0.05O3-d sample (28%oftheoretical).Proton conductivity was studied on pre-hydrated samples(under both dry and wetAr atmospheres).Thebulk proton conductivities of the heating cycle of pre-hydrated BaZr0.9In0.05M0.05O3-d (M ¼ Ga3+ or Yb3+) samples were 2.1 * 10-5 S cm-1 and 1.9 * 10-4 Scm-1 at 350C, respectively.The effect of co-doping onproton conductivity was investigatedand the results are compared with single doped systems e.g. BaZr0.9M0.1O3-d (M=Ga3+, In3+ orYb3+) samples.
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| 2. |
- Hull, S., et al.
(författare)
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High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2
- 2011
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 184:11, s. 2925-2935
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Tidskriftsartikel (refereegranskat)abstract
- The structural properties of the binary alkaline-earth halides SrCl(2), SrBr(2), BaCl(2) and BaBr(2) have been investigated from ambient temperature up to close to their melting points, using the neutron powder diffraction technique. Fluorite-structured SrCl(2) undergoes a gradual transition to a superionic phase at 900-1100 K, characterised by an increasing concentration of anion Frenkel defects. At a temperature of 920(3) K, the tetragonal phase of SrBr(2) undergoes a first-order transition to a cubic fluorite phase. This high temperature phase shows the presence of extensive disorder within the anion sublattice, which differs from that found in superionic SrCl(2), BaCl(2) and BaBr(2) both adopt the cotunnite crystal structure under ambient conditions. BaCl(2) undergoes a first-order structural transition at 917(5) K to a disordered fluorite-structured phase. The relationship between the (disordered) crystal structures and the ionic conductivity behaviour is discussed and the influence of the size of the mobile anion on the superionic behaviour is explored.
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| 3. |
- Hull, Stephen, et al.
(författare)
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Oxygen vacancy ordering within anion-deficient Ceria
- 2009
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 182:10, s. 2815-2821
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Tidskriftsartikel (refereegranskat)abstract
- The structural properties of anion deficient ceria, CeO2-delta, have been studied as a function of oxygen partial pressure, p(O-2), over the range 0 >= log(10)p(O-2) >= -18.9 at 1273(2) K using the neutron powder diffraction technique. Rietveld refinement of the diffraction data collected on decreasing p(O-2) showed increases in the cubic lattice parameter, a, the oxygen nonstoichiometry, delta, and the isotropic thermal vibration parameters, u(Ce) and u(O), starting at log(10)p(O-2)similar to-11. The increases are continuous, but show a distinct kink at log(10)p(O-2)similar to-14.5. Analysis of the total scattering (Bragg plus diffuse components) using reverse Monte Carlo (RMC) modelling indicates that the O2- vacancies preferentially align as pairs in the cubic directions as the degree of nonstoichiometry increases. This behaviour is discussed with reference to the chemical crystallography of the CeO2-Ce2O3 system at ambient temperature and, in particular, to the nature of the long-range ordering of O2- vacancies within the crystal structure of Ce7O12. (C) 2009 Elsevier Inc. All rights reserved.
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| 4. |
- KINYANJUI, FRANCIS GACHAO, 1981, et al.
(författare)
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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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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:14, s. 5088-5101
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Tidskriftsartikel (refereegranskat)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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| 5. |
- KINYANJUI, FRANCIS GACHAO, 1981, et al.
(författare)
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In-situ conductivity and hydration studies of proton conductors using neutron powder diffraction
- 2012
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 225, s. 312-316
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Tidskriftsartikel (refereegranskat)abstract
- An impedance spectroscopy cell and humidifier system has been developed to study the ion conducting properties and hydration/dehydration reactions in-situ during neutron powder diffraction experiments. As a model system, acceptor doped barium zirconate, BaZr0.5In0.5O2.75, has been studied during in-situ hydration and dehydration. Rietveld refinement of the collected data shows an increase in lattice parameter, a, upon hydration of BaZr0.5In0.5O2.75. In addition, we show the existence of a two-phase region, containing deuterated and non-deuterated barium zirconate, in the temperature interval ~ 573 K to ~ 873 K. Impedance spectroscopy data collected in-situ on heating and cooling and the corresponding ionic conductivity agree well with the change in deuteron content, as determined from neutron diffraction as a function of temperature. The newly developed in-situ cells make it possible to correlate conducting properties to structural changes under identical conditions and will have applicability to many other proton conducting solids.
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| 6. |
- Norberg, Stefan, 1972, et al.
(författare)
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Local structure and ionic conductivity in the Zr2Y2O7-Y3NbO7 system
- 2009
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:21, s. 215401-
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Tidskriftsartikel (refereegranskat)abstract
- The Zr0.5-0.5xY0.5+0.25xNb0.25xO1.75 solid solution possesses an anion-deficient fluorite structure across the entire 0
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| 7. |
- Norberg, Stefan, 1972, et al.
(författare)
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Pyrochlore to Fluorite Transition: The Y2(Ti1-xZrx)2O7 (0.0 ≤ x ≤ 1.0) System
- 2012
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 24:22, s. 4294-4300
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Tidskriftsartikel (refereegranskat)abstract
- The structural properties of the system Y-2(Ti1-xZrx)(2)O-7 have been investigated using the neutron powder diffraction technique, including a detailed analysis of the "total scattering" using reverse Monte Carlo modeling to probe the short-range ion-ion correlations over sample range 0.0
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| 8. |
- Norberg, Stefan, 1972, et al.
(författare)
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Structural Disorder in Doped Zirconias, Part I: The Zr0.8Sc0.2-xYxO1.9 (0.0 ≤x ≤ 0.2) System
- 2011
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:6, s. 1356-1364
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Tidskriftsartikel (refereegranskat)abstract
- The influence of local ordering of the anion vacancies and cation-anion vacancy interactions on the ionic conductivity of the anion-deficient fluorite Zr0.8Sc0.2-xYxO1.9 (0.0 directions. Significantly, an increased proportion of the oxygen vacancies are associated with the Zr4+ cations in Zr0.8Y0.2O1.9, while in Zr0.8Sc0.2O1.9 they show no significant preference for being nearest neighbor to a Sc3+ or a Zr4+ cation. Thus, it is concluded that the lower ionic conductivity at x = 0.2 is predominantly a consequence of the larger size of the Y3+ cation, which induces strain in the lattice and hinders diffusion of the O2-, rather than changes in the local ordering of the anion vacancies.
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| 9. |
- Ahmed, Istaq, 1972
(författare)
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Acceptor-Doped BaZrO3 Perovskite: Synthesis, Structure and Proton Conductivity.
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acceptor-doped perovskite oxides exhibit significant proton conductivity in hydrogen containing atmospheres. Therefore, they have potential for use as separator materials for various electrochemical devices including gas sensors, electrolysers and fuel cells. For example, yttrium doped BaZrO3 perovskites have shown high bulk proton conductivity and high chemical stability. However, significant grain boundary resistance has subdued the technological applications.The work constituting this thesis has mainly been focused on synthesis, structural characterisation and electrochemical investigations of acceptor-doped BaZr1-xMxO3-d (M = Ga3+, Sc3+, In3+, Yb3+ and Y3+: x = 0-0.75) perovskite oxides in bulk form. The polycrystalline samples were prepared via a traditional solid-state sintering route and by wet chemical routes. A combination of techniques such as x-ray and neutron powder diffraction, thermogravimetry, scanning electron microscopy (SEM) and impedance spectroscopy (IS) have been used to characterize the samples. Rietveld analysis of high resolution low temperature neutron powder diffraction data revealed that the deuteron site was localised at, or close to, the 12h crystallographic position of BaZr0.5In0.5O2.5(OD)0.5. It was also confirmed that the hydration/deuteration reaction caused an expansion of the cell parameter, while keeping the lattice symmetry, and thus the basic structure intact. Moreover, from Rietveld analysis of the neutron data the oxygen vacancy concentration was determined and they were found to be statistically distributed in the structure. Heavily doped samples showed higher proton conductivity compared to lightly doped samples, indeed this is an option to improve the conductivity in the material for certain dopants, e.g., In, Sc and Yb. Interestingly, at the same level of doping the proton conductivity differs significantly for different acceptors dopants. The effects of co-doping at the B-site, e.g. BaZr0.9In0.05M0.05O3-d (M = Ga and Yb) were investigated. Surprisingly, lower proton conductivity was obtained for these co-doped samples compared to the sample containing a single dopant ion e.g. BaZr0.9M0.1O3-d (M = Ga, In and Yb).It was also confirmed that samples with smaller grain size show lower total proton conductivity due to high grain-boundary resistance.Through the present work an increased understanding of the factors influencing the proton conductivity in acceptor doped BaZrO3 has been obtained. In particular, the highly doped materials were found to be of considerable interest in the effort of producing materials with high proton conductivity.
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| 10. |
- Ahmed, Istaq, 1972, et al.
(författare)
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Crystal structure and proton conductivity of BaZr0.9Sc0
- 2008
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Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 91:9, s. 3039-3044
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Tidskriftsartikel (refereegranskat)abstract
- Solid-state sintering has been used to prepare the perovskite BaZr0.9Sc0.1O3-delta. Analysis of X-ray powder diffraction data shows that an increase of the unit cell parameter, a, was observed after deuteration. Rietveld analysis of room-temperature neutron powder diffraction data confirmed cubic symmetry (space group Pm-3m). Dynamic thermogravimetric analysis indicates that the hydration process occurs below 335 degrees C and approximately 58% of the theoretical number of protonic defects can be filled. The presence of protons/deutrons is seen from the strong O-H/O-D stretch band in the infrared spectrum of the hydrated/deuterated samples. The proton conductivity of a prehydrated sample was investigated under dry and wet Ar atmospheres
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