SwePub - sökning: WFRF:(Ahmed Istaq 1972)

Numrering	Referens	Omslagsbild	Hitta
1.	Ahmed, Istaq, 1972, et al. (författare) Effect of co-doping on proton conductivity in perovskite oxides BaZr0.9In0.05M0.05O3−δ (M = Yb3+ or Ga3+) 2010 Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 35:12, s. 6381-6391 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.
2.	Hull, S., et al. (författare) High temperature crystal structures and superionic properties of SrCl2, SrBr2, BaCl2 and BaBr2 2011 Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 184:11, s. 2925-2935 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.
3.	Hull, Stephen, et al. (författare) Oxygen vacancy ordering within anion-deficient Ceria 2009 Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 182:10, s. 2815-2821 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.
4.	KINYANJUI, FRANCIS GACHAO, 1981, et al. (författare) Crystal structure and proton conductivity of BaSn0.6Sc0.4O3-delta: insights from neutron powder diffraction and solid-state NMR spectroscopy 2016 Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:14, s. 5088-5101 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.
5.	KINYANJUI, FRANCIS GACHAO, 1981, et al. (författare) In-situ conductivity and hydration studies of proton conductors using neutron powder diffraction 2012 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 225, s. 312-316 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.
6.	Norberg, Stefan, 1972, et al. (författare) Local structure and ionic conductivity in the Zr2Y2O7-Y3NbO7 system 2009 Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:21, s. 215401- 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
7.	Norberg, Stefan, 1972, et al. (författare) Pyrochlore to Fluorite Transition: The Y2(Ti1-xZrx)2O7 (0.0 ≤ x ≤ 1.0) System 2012 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 24:22, s. 4294-4300 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
8.	Norberg, Stefan, 1972, et al. (författare) Structural Disorder in Doped Zirconias, Part I: The Zr0.8Sc0.2-xYxO1.9 (0.0 ≤x ≤ 0.2) System 2011 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:6, s. 1356-1364 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.
9.	Ahmed, Istaq, 1972 (författare) Acceptor-Doped BaZrO3 Perovskite: Synthesis, Structure and Proton Conductivity. 2008 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.
10.	Ahmed, Istaq, 1972, et al. (författare) Crystal structure and proton conductivity of BaZr0.9Sc0 2008 Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 91:9, s. 3039-3044 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
11.	Ahmed, Istaq, 1972, et al. (författare) Improved Proton Conductivity in Spark-Plasma Sintered Dense Ceramic BaZr0.5In0.5O3-delta 2010 Ingår i: Electrochemical and Solid State Letters. - : The Electrochemical Society. - 1099-0062 .- 1944-8775. ; 13:11 Tidskriftsartikel (refereegranskat)abstract Spark-plasma sintering method was used to prepare dense proton conducting perovskite oxide BaZr0.5In0.5O3-delta. Analysis of X-ray powder diffraction data showed that the sample adopt the cubic crystal structure having the space group Pm3m. Thermogravimetric analysis of prehydrated samples showed significant mass losses beyond 300 degrees C due to loss of protons as water vapor. Scanning electron microscope images show that the grain size of the spark-plasma sintered dense sample was smaller than that of solid-state sintered porous sample. The highest total proton conductivity (2 X 10(-3) S cm(-1) at 450 degrees C) was found for dense spark-plasma sintered sample under wet H-2 than the samples prepared by other routes.
12.	Ahmed, Istaq, 1972, et al. (författare) Influence of Microstructure on Electrical Properties in BaZr0.50In0.50O3-δ Proton Conductor 2008 Ingår i: Solid State Ionics. ; 179, s. 3480-3485 Tidskriftsartikel (refereegranskat)
13.	Ahmed, Istaq, 1972, et al. (författare) Influence of microstructure on electrical properties in BaZr0.5In0.5O3-delta proton conductor 2008 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 179:21-26, s. 1155-1160 Tidskriftsartikel (refereegranskat)abstract Two different preparative routes, one a wet chemical route (WCR) and the other a traditional solid state sintering route (SSR), have been used to synthesise the oxygen deficient perovskite BaZr0.5In0.5O3-delta. Analysis of X-ray powder diffraction data showed that both phases adopt cubic crystal structures. Environmental scanning electron microscope (ESEM) images showed that a smaller grain size was obtained for the WCR sample. Dynamic then-no-gravimetric analysis indicated significant mass losses for hydrated samples compared to their respective dried samples. Proton conductivity was investigated for hydrated and as-prepared phases under dry and wet atmospheres, respectively. The hydrated sample prepared via the solid state sintering route displayed a higher proton conductivity under dry conditions, reflecting the presence of fewer grain boundaries in this sample. (c) 2008 Elsevier B.V. All rights reserved
14.	Ahmed, Istaq, 1972, et al. (författare) Location of deuteron sites in the proton conducting perovskite BaZr0.50In0.50O3-y 2008 Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 450:1-2, s. 103-110 Tidskriftsartikel (refereegranskat)abstract High-resolution neutron powder diffraction data have been collected on deuterated and dried samples of the perovskite BaZr0.5In0.5O2.75 at 5 K and room temperature, respectively. Inspection of Fourier nuclear density maps for the deuterated phase have allowed the deuteron position to be refined on a 12h (1/2, y, 0) crystallographic site, with y = 0.217(4) yielding a chemically reasonable O-D distance of 0.92(2) angstrom. Evidence for anisotropy of the deuteron position is also found consistent with a 24k crystallographic site (0.56, 0.21, 0) indicative of displacements of the ion towards neighbouring oxygen ions. The presence of static oxygen disorder in both the dried and deuterated samples is apparent from the structural analyses. Raman spectra confirm short range deviations from cubic symmetry for both dried and hydrated samples.
15.	Ahmed, Istaq, 1972, et al. (författare) Proton conduction in Perovskite Oxide BaZr0.5Yb0.5O3-δ Prepared by Wet Chemical Route 2008 Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 155:11, s. 97-102 Tidskriftsartikel (refereegranskat)abstract A wet chemical route has been used to synthesize the oxygen deficient perovskite Ba Zr0.5 Yb0.5 O3-δ. Analysis of X-ray powder diffraction data showed that both dried and hydrated samples adopt cubic crystal structures of space group Pm 3- m. Dynamic thermogravimetric analysis showed a significant mass loss for the hydrated sample compared to the dried sample, indicating that ∼28% of the oxygen vacancies are filled by protonic defects. The strong O-H stretch band, 2500-3500 cm-1, in the IR absorbance spectrum also clearly manifests the presence of significant levels of protons in the hydrated material. Proton conductivity was investigated on prehydrated (under dry Ar) and as-prepared (under wet Ar) samples. The heating cycle of the prehydrated sample showed higher proton conductivity compared to the cooling cycle, especially in the intermediate temperature range (150-550°C). Finally, comparison with data for Ba Zr0.9 Yb0.1 O3-δ revealed that the more heavily doped sample showed higher proton conductivity compared to the more lightly doped sample. © 2008 The Electrochemical Society.
16.	Ahmed, Istaq, 1972, et al. (författare) Proton conductivity and low temperature structure of In-doped BaZrO3 2006 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 177:26-32, s. 2357-2362 Tidskriftsartikel (refereegranskat)abstract The proton conductivity and structural features of In3+ substituted BaZrO3 samples, i.e., BaZr1−xInxO3−δ, were investigated. Rietveld analysis of low temperature (10 K) neutron powder diffraction data collected on as-prepared and deuterated samples confirmed cubic symmetry (space group Pm-3m) for all compositions. The level of oxygen vacancies refined in the as-prepared samples were in good agreement with the values expected to conserve charge neutrality, whilst an increase in oxygen occupancy, reflecting the incorporation of OD− species, was obtained for the deuterated materials. An expansion of the unit cell parameter, a, was observed as a function of In3+ doping as well as after the deuteration reaction. The conductivity of pre-hydrated and dry samples was measured using impedance methods. For 25% In-doped BaZrO3, the low T (300 °C) conductivity of the heating cycle of the dried sample was greater than that of the cooling cycle of the pre-hydrated sample indicating a greater number of protons in the nominally dry sample. In contrast, the conductivity values were similar at higher temperatures e.g. T > 500 °C where proton conduction is not dominant.
17.	Ahmed, Istaq, 1972, et al. (författare) Proton conductivity and low temperature structure of In-doped BaZrO3 2006 Ingår i: Solid State Ionics. ; 177, s. 2357- Tidskriftsartikel (refereegranskat)
18.	Ahmed, Istaq, 1972, et al. (författare) Proton Conductivity in Mixed B-Site Doped Perovskite Oxide BaZr[sub 0.5]In[sub 0.25]Yb[sub 0.25]O[sub 3 - delta] 2010 Ingår i: Journal of The Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 157:12 Tidskriftsartikel (refereegranskat)abstract A wet chemical route was used to prepare the oxygen deficient codoped perovskite oxide BaZr0.5In0.25Yb0.25O3−. Analysis of X-ray powder diffraction data showed that the sample belongs to the cubic crystal system with space group Pmm. Dynamic thermogravimetric (TG) analysis confirmed complete filling of oxygen vacancies (V) by protonic defects (OH) during the hydration process. The proton conductivity was investigated by impedance spectroscopy. The bulk and total conductivities of prehydrated BaZr0.5In0.25Yb0.25O3− were found to be 8.5×10−4 and 2.2×10−5 S cm−1, respectively, at 300°C. The total conductivity in the codoped perovskite oxide was higher compared to that of the respective single doped perovskite oxides with the same doping level. The bulk and grain-boundary mobility and diffusion coefficients of protons were calculated at 200°C using impedance and TG data to obtain the conductivity and proton concentration, respectively. The high bulk diffusivity (2.3×10−7 cm2 s−1) was obtained which indicates that the protons are more free to move in the heavily doped matrix compared to the lightly doped systems where trapping of protons occurs.
19.	Ahmed, Istaq, 1972 (författare) Some BaZrO3 Based Proton Conductors: Synthesis, Structure and Conductivity 2006 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)
20.	Ahmed, Istaq, 1972, et al. (författare) Structural study and proton conductivity in Yb-doped BaZrO3 2007 Ingår i: Solid State Ionics. - 0167-2738. ; 178:(7-10), s. 515-520 Tidskriftsartikel (refereegranskat)abstract Traditional solid state sintering has been used to prepare the perovskite BaZr0.9Yb0.1O3-delta. Analysis of X-ray powder diffraction data shows that an increase of the unit cell parameter, a, was observed compared to undoped BaZrO3. Rietveld analysis of room temperature neutron powder diffraction data confirmed cubic symmetry (space group Pm-3m). Dynamic thermogravimetric analysis (TGA) indicates that the hydration process occurs below 200 degrees C. The strong O-H stretch band, 2500-3500 cm(-1), in the infrared absorbance spectrum clearly manifests the presence of protons in the hydrated material. Proton conductivity was investigated on hydrated and as-prepared samples under dry and wet atmospheres, respectively. Keywords: X-ray diffraction; neutron diffraction; Rietveld refinement; proton conductor; perovskite
21.	Ahmed, Istaq, 1972, et al. (författare) Structural study and proton conductivity of BaZr0.90Ga0.10O2.95 2006 Ingår i: Advances of Solid Oxide Fuel Cells II, Ceramic Engineering and Science Proceedings. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. ; 27:4, s. 105-117 Tidskriftsartikel (refereegranskat)abstract Traditional solid state sintering has been used to prepare the perovskite BaZr0.9Ga0.1O2.95. Analysis of X-ray powder diffraction data shows that a decrease of the unit cell parameter a was observed compared to the undoped BaZrO3, which confirms successful substitution of Ga3+ for Zr4+ at the B site. Rietveld analysis of room temperature neutron powder diffraction data confirmed cubic symmetry (space group Pm-3m) for both as- prepared and deuterated BaZr0.90Ga0.10O2.95 samples. The strong O-H stretch band (2500-3500 cm−1) in the infrared absorbance spectrum clearly manifests the presence of protons in the pre-hydrated material. The bulk and total conductivities of prehydrated BaZr0.9Ga0.1O2.95 are 1.17 × 10−5 and 3.55 × 10−6 Scm−1, respectively at 400°C, which are more than one order of magnitude higher than for dried a sample at the same temperature. In contrast, the total conductivity of pre-hydrated and dried samples is similar at higher temperature, e. g. T > 800 °C. The higher activation energy (e. g. 0.7 eV) for pre-hydrated sample compared to typical value (0.4-0.5 eV) of proton conduction may suggest that the protons are trapped in the material.
22.	Ahmed, Istaq, 1972, et al. (författare) Structural Study and Proton Conductivity of BaZr0.90Ga0.10O2.95 2006 Ingår i: Advances of Solid Oxide Fuel cells II, Ceramic Engineering and Science Proceedings. ; 27:4, s. 105-117 Konferensbidrag (refereegranskat)
23.	Ahmed, Istaq, 1972, et al. (författare) Synthesis and structural characterization of perovskite type proton conducting BaZr1-xInxO3-delta (0.0 <= x <= 0.75) 2006 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 177:17-18, s. 1395-1403 Tidskriftsartikel (refereegranskat)abstract Solid state sintering has been used to prepare the cubic perovskite structured compounds BaZr1-xInxO3-delta (0.0 <= x <= 0.75). Analysis of X-ray powder diffraction (XRPD) data reveals that the unit cell parameter, a, increases linearly with an increased Indium concentration. XRPD data was also used to demonstrate the completion of sample hydration, which was reached when the materials showed a set of single-phase Bragg-peaks. Dynamic thermogravimetric analysis (TGA) data showed that approx. 89% of the total number of available oxygen vacancies can be filled in BaZr1-xInxO3-delta for x=0.50, and that the maximum water uptake occurs below 300 degrees C. Rietveld analysis of the room temperature neutron powder diffraction (NPD) data confirmed the average cubic symmetry (space group Pm-3m), and an expansion of the unit cell parameter after the hydration reaction. The strong O-H stretch band, 2500-3500 cm(-1), in the infrared absorbance spectrum clearly manifests the presence of protons in the hydrated material. Proton conductivity of hydrated BaZr1-xInxO3-delta, x=0.75 was investigated during heating and cooling cycles under dry argon atmosphere. The total conductivity during the heating cycle was nearly two orders of magnitude greater than that of cooling cycle at 300 degrees C, whilst these values were similar at higher temperatures i.e. T > 600 degrees C.
24.	Besikiotis, V., et al. (författare) Crystal structure, hydration and ionic conductivity of the inherently oxygen-deficient La2Ce2O7 2012 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 228, s. 1-7 Tidskriftsartikel (refereegranskat)abstract The crystal structure, hydration and ionic conductivity of the inherently oxygen deficient La2Ce2O7 system have been investigated. On the basis of Rietveld analysis of neutron diffraction data, the material is found to adopt a cation disordered oxygen-deficient fluorite structure. Impedance spectroscopy, performed in the temperature range 1000-200 degrees C and as a function of water vapor and oxygen partial pressure, suggests that oxide ion conductivity dominates at high temperatures, while protons are the main charge carrier at temperatures below approximately 450 degrees C. Proton conductivity was confirmed by isotope shifts under H2O and D2O. The dissolution of water was measured by means of thermogravimetry (TG). A defect chemical model is developed to derive hydration thermodynamic parameters based on TG and conductivity data. The hydration enthalpy was, moreover, determined directly by simultaneous TG and differential scanning calorimetry (TG-DSC). The TG-DSC values were in good agreement with those modeled from conductivity and TG data.
25.	Bjorheim, T. S., et al. (författare) A combined conductivity and DFT study of protons in PbZrO3 and alkaline earth zirconate perovskites 2010 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 181:3-4, s. 130-137 Tidskriftsartikel (refereegranskat)abstract The electrical properties of nominally undoped and 4 mol% Y-doped PbZrO3 have been investigated by AC conductivity measurements and impedance spectroscopy under various p(H2)O and p(O2) at high temperatures. The results indicate that the defect structures are dominated by acceptors (Y dopant and/or Pb vacancies formed during synthesis). In dry atmosphere and at high temperatures, the acceptors are compensated by oxygen vacancies. These are hydrated and replaced by protonic defects (hydroxide ions on oxide ion sites) at higher p(H2)o and lower temperatures. In oxidizing atmospheres, a minority concentration of electron holes dominates the conductivity. At lower temperatures and in wet atmosphere, a significant protonic conductivity contribution is also observed. Based on p(O2) and p(H2)o isotherms, a model for incorporation of protonic defects has been applied, and the standard enthalpy of hydration of oxygen vacancies in undoped PbZrO3 has been determined (-1.07 +/- 0.13 eV). The measured total conductivities are influenced by high grain boundary resistance. Hence, the enthalpy is at the present stage assigned to the polycrystalline ceramic material as such. Rough estimates of bulk proton mobility in Y-doped PbZrO3 yield u(H)(0)+ = 17 cm(2)K/Vs and Delta H-m,H(+) = 0.93 eV. A complementary DFT study of the hydration thermodynamics of PbZrO3 and the alkaline earth zirconate perovskites AZrO(3) (A = Ca, Sr, Ba) is also reported. The experimental and theoretical hydration enthalpies are compared with those of other ABO(3) perovskites. Correlations between the hydration thermodynamics and other properties of the materials are discussed. (C) 2009 Elsevier B.V. All rights reserved.
26.	Eurenius, Karinh, 1980, et al. (författare) Investigation of proton conductivity in Sm1.92Ca0.08Ti2O7 − δ and Sm2Ti1.92Y0.08O7 − δ pyrochlores 2010 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 181:3-4, s. 148-153 Tidskriftsartikel (refereegranskat)abstract The results of the synthesis and characterisation of pyrochlore systems Sm1.92Ca0.08Ti2O7 − δ and Sm2Ti1.92Y0.08O7 − δ are reported. The electrical conductivity of the materials was studied using impedance spectroscopy under wet and dry oxygen and argon. Enhancements of the bulk conductivity at temperatures up to 500 °C were observed for wet conditions indicative of significant proton conductivity. The presence of dissolved protons in the materials is supported by thermogravimetric analysis and infrared spectroscopy. Proton conduction was confirmed by measurements in O2/D2O and Ar/D2O. The results reveal the importance of the correct choice of dopant site for the pyrochlore structure, with A-site substitution yielding the highest levels of proton, as well as oxide ion, conduction. For both samples bulk, rather than grain boundary, conduction is found to be dominant.
27.	Karlsson, Maths, et al. (författare) Dopant Concentration and Short-Range Structure Dependence of Diffusional Proton Dynamics in Hydrated BaInxZr1-xO3-x/2 (x=0.10 and 0.50) 2010 Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:7, s. 3292-3296 Tidskriftsartikel (refereegranskat)abstract We investigate proton self-dynamics in the acceptor-doped and hydrated proton-conducting perovskite-type oxides BaInxZr1-xO3-x/2 (x = 0.10 and 0.50) on a microscopic length scale for temperatures in the range 470-525 K, using neutron spin-echo spectroscopy. For the highly doped material (x = 0.50), we observe a wide range of translational diffusional rates of the protons in the Structure, oil the nanosecond time scale and with in effective activation energy of about 0.75 eV. The wide distribution of diffusional rates is related to the In-doping, which creates local structural distortions or the average Cubic Structure and thus many structurally different Configurations of the protons, each with slightly different energy barriers for the protonic motion. For the weakly doped material (x = 0.10), which has a more ordered local Structure, the results show proton dynamics oil a Much more well-defined time scale, similar to 60 ps at 500 K, but also Suggest that a significant part of the protons ill the Structure are "immobile" within the experimental neutron spin-echo time window (similar to 5 ps to 1.3 ns). Furthermore, the results indicate that the dopant atoms affect the proton diffusion ill a nonlocalized manner and not as well-localized trapping centers.
28.	Karlsson, Maths, 1978, et al. (författare) O-H wag vibrations in hydrated BaInxZr1-xO3-x/2 2008 Ingår i: Physical Review B. ; 77, s. 104302- Tidskriftsartikel (refereegranskat)
29.	Karlsson, Maths, 1978, et al. (författare) Quasielastic neutron scattering of hydrated BaZr0.90A0.10O2.95 (A = Y and Sc) 2009 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 180:1, s. 22-28 Tidskriftsartikel (refereegranskat)abstract Proton motions in hydrated proton conducting perovskites BaZr 0.90 A 0.10 O 2.95 (A = Y and Sc) have been investigated using quasielastic neutron scattering. The results reveal a localized motion on the ps time scale and with an activation energy of ~ 10-30 meV, in both materials. The temperature dependence of the total mean square displacement of the protons shows an onset of this motion at a temperature of about 300 K. The low activation energy, much lower than the activation energy for the macroscopic proton conductivity, suggests that this motion is not the rate-limiting process for the long-range proton diffusion, i.e. it is not linked to the two materials significantly different proton conductivities. In fact, a comparison of the QENS results with density functional theory calculations indicates that for both materials the observed motion may be ascribed to intra-octahedral proton transfers occurring close to a dopant atom. © 2008 Elsevier B.V. All rights reserved.
30.	Karlsson, Maths, et al. (författare) Short-range structure of proton-conducting BaM0.10Zr0.90O2.95 (M = Y, In, Sc and Ga) investigated with vibrational spectroscopy 2010 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 181:3-4 (Sp. Iss.), s. 126-129 Tidskriftsartikel (refereegranskat)abstract The short-range structures of hydrated and dry samples of the proton-conducting, cubic-structured, acceptor-doped perovskites BaM0.10Zr0.90O2.95 (M=Y, In, Sc and Ga), and, for comparison, BaZrO3, have been investigated using infrared and Raman spectroscopy. The results show that the acceptor-doping leads to local structural distortions of the average cubic structure, most likely related to tilts of (M/Zr)O-6 octahedra, and that the distortions are most pronounced in the Ga-doped material for which we also find additional distortions upon hydration. For the Y-, In- and Sc-doped equivalents the distortions are somewhat weaker and hydration is found to have a reversed, although weak, effect. A comparison of the spectroscopic results to the reported proton diffusivities of the investigated materials would suggest that the much lower proton diffusivity in the Ga-doped material is associated to its stronger structural distortions. (C) 2009 Elsevier B.V. All rights reserved.
31.	Karlsson, Maths, et al. (författare) Short-range structure of proton-conducting perovskite BaInxZr1-xO3-x/2 (x=0-0 2009 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:10, s. 3480-3486 Tidskriftsartikel (refereegranskat)abstract In a systematic study, we investigate the effect of dopant level and hydration on the short-range structure of the proton-conducting perovskite-type oxide BaInxZr1-xO3-x/2 (x = 0 - 0.75), using infrared and Raman spectroscopy. The results show that the doping leads to significant local distortions of the average cubic structure of these materials. By increasing the In concentration from x = 0 to x = 0.75, new bands appear and grow in intensity in both the IR and the Raman spectra, showing that the local distortions become successively more and more pronounced. The structural distortions are largely uncorrelated to the presence of oxygen vacancies, but instead are mainly driven by the size and charge difference between the In3+ and Zr4+ ions, which leads to displacements of the cations and to tilting of the (In/Zr)O-6 octahedra. On the basis of our results, we suggest that there is a threshold between x = 0.10 and x = 0.25 where the structural distortions propagate throughout the whole perovskite structure. Comparison of our spectroscopic data with the proton conductivity for the same materials indicates that the presence of extended structural distortions is favorable for fast proton transport.
32.	Karlsson, Maths, et al. (författare) Temperature-Dependent Infrared Spectroscopy of Proton-Conducting Hydrated Perovskite BaInxZr1-xO3-x/2 (x=0.10-0.75) 2010 Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:13, s. 6177-6181 Tidskriftsartikel (refereegranskat)abstract We investigate the temperature dependence of the O-H stretch band in the infrared absorbance spectra of the proton-conducting hydrated perovskites BaInxZr1-xO3-x/2 (x = 0.10-0.75) over the temperature range -160 to 350 degrees C. Upon increasing temperature from -160 to 30 degrees C, we show that there is a redistribution of protons from nonsymmetrical structural configurations, such as Zr-OH-In and Zr-OH-Zr-vacancy, where the degree of hydrogen bonding between the protons and neighboring oxygens is strong, to symmetrical configurations, such as Zr-OH-Zr and In-OH-In, where hydrogen bonding is weaker. Spectra measured at elevated temperatures, 30-350 degrees C, indicate preferential desorption of protons in sites where the degree of hydrogen bonding is strong, and show that the materials gradually dehydrate with increasing temperature. The dehydration rate is found to be highest in the temperature range 275-325 degrees C. Furthermore, the spectroscopic results indicate that strong hydrogen bonding, caused by dopant-induced short-range structural distortions, is favorable for high proton mobility and that the rate-limiting step in the conduction mechanism is the proton transfer between neighboring oxygens.
33.	Karlsson, Maths, 1978, et al. (författare) Using Neutron Spin-Echo To Investigate Proton Dynamics in Proton-Conducting Perovskites 2010 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 22:3, s. 740-742 Tidskriftsartikel (refereegranskat)abstract The applicability and potential of neutron spin-echo (NSE) to study proton dynamics in proton-conducting ceramics was studied. The experiment was performed on hydrated BaZr 0,90 Y 0.10 O 2.95 (10Y:BZO), a cubic perovskite with a relatively high proton conductivity. The NSE experiment was performed at the IN15 spectrometer at Institut Laue-Langevin (ILL) in Grenoble, France. The relaxation rate for two Q-values for the temperature 563 K was determined. The first-principles calculations were carried out within the framework of density functional theory (DFT). The calculated diffusion harriers far from Y-dopants are found to he 0.20 and 0.18 eV for the proton transfer and hydroxyl rotation motion, respectively. The binding energy to a Y-dopant is 0.16 eV, and the influence of the Y-dopant on the energetics for the proton is quite extended in space, including both the first and the second coordination shells.
34.	Karlsson, Maths, 1978, et al. (författare) Vibrational Properties of Protons in Hydrated BaInxZr1-xO3-x/2 2005 Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 72, s. 1-7 Tidskriftsartikel (refereegranskat)abstract We investigate the local proton dynamics in the proton conducting hydrated perovskite system BaInxZr1-xO3-x/2 (x=0.25-0.75) using infrared spectroscopy and first-principles calculations. We show that oxygen vacancies and dopant atoms in the vicinity of the proton tilt the proton toward a neighboring oxygen creating strongly hydrogen-bonded configurations. This is manifested as a strong redshift of the O-H stretch band in the infrared absorption spectrum. We also find considerable fluctuations of the nearest and next-nearest oxygen-proton distances with time, resulting in additional spectral broadening. By comparing the frequencies of computed O-H stretch modes we can relate specific local configurations to different parts of the broad O-H stretch band. Even though hydrogen-bonded configurations favor proton transfer they hinder the long-range migration by decreasing the reorientational rate. Thus, in order to optimize the proton mobility it is important to avoid extreme configurations caused by either oxygen vacancies or dopant atoms in the perovskite structure.
35.	Larsson, Carl Fredrik, 1980, et al. (författare) Overcurrent Abuse of Primary Prismatic Zinc–Air Battery Cells Studying Air Supply Effects on Performance and Safety Shut-Down 2017 Ingår i: Batteries. - : MDPI AG. - 2313-0105. ; 3:1 Tidskriftsartikel (refereegranskat)abstract Overcurrent abuse has been performed on commercial 48 Ah primary prismatic zinc (Zn)–Air battery cells with full air supply as well as with shut-off air supply. Compared to other battery technologies, e.g., lithium-ion batteries, metal–air batteries offer the possibility to physically stop the battery operation by stopping its air supply, thus offering an additional protection against severe battery damage in the case of, e.g., an accidental short circuit. This method may also reduce the electrical hazard in a larger battery system since, by stopping the air supply, the voltage can be brought to zero while maintaining the energy capacity of the battery. Measurements of overdischarge currents and current cut-off by suffocation have been performed to assess the safety of this type of Zn–air battery. The time to get to zero battery voltage is shown to mainly be determined by the volume of air trapped in the cell.
36.	Liu, J. J., et al. (författare) Application of combined neutron diffraction and impedance spectroscopy for in-situ structure and conductivity studies of La2Mo2O9 2011 Ingår i: Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 269:5, s. 539-543 Tidskriftsartikel (refereegranskat)abstract In-situ neutron diffraction combined with AC impedance spectroscopy was applied successfully to investigate the correlation between crystal structure and electrical properties of the La2Mo2O9 oxide ion conducting electrolyte material. Neutron diffraction patterns were collected as a function of temperature while the AC impedance spectra were recorded simultaneously using a modified sample environment to monitor the conductivity change of the sample. A close relationship between unit cell parameters and the bulk conductivity was observed, confirming that the oxygen transport is dependent on the lattice structure. With the transition from the low temperature alpha to the high temperature beta phase, expansion of the crystal structure makes more space available for oxygen transport, leading to a dramatic increase of the ionic conductivity. The successful application of this technique provides a new method to simultaneously investigate crystal structure and electrical properties in electro-ceramics in the future.
37.	Magraso, A., et al. (författare) In situ high temperature powder neutron diffraction study of undoped and Ca-doped La28-xW4+xO54+3x/2 (x=0.85) 2013 Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 1:11, s. 3774-3782 Tidskriftsartikel (refereegranskat)abstract In situ neutron diffraction experiments of 2% Ca-doped and nominally undoped lanthanum tungstate (La28-xW4+xO54+3x/2, with x = 0.85) have been carried out under controlled pD(2)O and pO(2) at elevated temperatures. All the diffraction patterns could be refined using an average cubic fluorite-related structure, in accordance with recent reports. The material exhibits disorder of the oxygen and the cation sublattices. Splitting of the oxygen sites around tungsten from the 32f to 96k Wyckoff position in the Fm (3) over barm space group improves the model and can better represent the oxygen disorder. No phase transition was detected from room temperature up to 800 degrees C under any of the studied conditions. Expansion of the unit cell constants in the presence of water at intermediate and low temperatures was correlated with the formation of protonic defects. The thermal expansion coefficient for lanthanum tungstate is rather linear under all studied conditions (similar to 11 x 10(-6) K-1). The in situ diffraction studies are correlated with dilatometry investigations and conductivity measurements.
38.	Park, Per-Ola, 1950, et al. (författare) Endoscopic sutured closure of a gastric natural orifice transluminal endoscopic surgery access gastrotomy compared with open surgical closure in a porcine model. A randomized, multicenter controlled trial. 2010 Ingår i: Endoscopy. - : Georg Thieme Verlag KG. - 1438-8812 .- 0013-726X. ; 42:4, s. 311-7 Tidskriftsartikel (refereegranskat)abstract In natural orifice transluminal endoscopic surgery (NOTES) procedures it is essential to be able to perform secure closure of the access perforation. The aim of this study was to compare endoscopically sutured closure of a gastric access gastrotomy using the tissue apposition system (TAS), with closure via laparotomy in a randomized multicenter study.
39.	Rahman, Seikh Mohammad Habibur, 1976, et al. (författare) 50 mol% indium substituted BaTiO3: Characterization of structure and conductivity 2012 Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 37:9, s. 7975-7982 Tidskriftsartikel (refereegranskat)abstract BaTi0.5In0.5O3-delta was prepared by solid state reaction at 1400 degrees C. Rietveld analysis of high resolution X-ray powder diffraction data indicated phase pure as-prepared material that adopts a cubic perovskite structure with a = 4.1536(1) angstrom. Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 57% of the theoretically achievable protonation was attained on exposure to a humid environment at 185 degrees C. After hydration the cell parameter increased to 4.1623(1) angstrom. Electrical conductivity was measured both with fixed and variable frequency ac impedance methods as a function of temperature, oxygen-, water vapour- and heavy water vapour partial pressures. In the temperature range 400-800 degrees C a slight increase in the total conductivity with increasing oxygen partial pressure is encountered, characteristic of a contribution from p-type charge carriers. The effect of the water vapour pressure on conductivity below 600 degrees C is much more prominent indicative of dominant proton conduction. At 300 degrees C the total conductivity in wet O-2 was estimated to be 9.30 x 10(-5) S/cm. At T > 800 degrees C the material is a pure oxide ion conductor.
40.	Rahman, Seikh Mohammad Habibur, 1976, et al. (författare) Characterisation of structure and conductivity of BaTi0.5Sc 0.5O3 - δ 2014 Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 255, s. 140-146 Tidskriftsartikel (refereegranskat)abstract BaTi0.5Sc0.5O3 - δ was prepared via solid state reaction route and final sintering at 1550 C. High resolution X-ray powder diffraction on the as-prepared material reveals a cubic perovskite structure with a unit cell parameter, a = 4.1343(1) Å. Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 74% of the theoretically achievable protonation through filling of oxide ion vacancies was attained on exposure to a humid environment at 185 C. Infrared spectroscopy revealed a broad OH stretching band confirming the presence of OHO • defects. Electrical conductivity was measured with variable frequency AC impedance methods in oxygen, argon, and hydrogen under dry, hydrated (H2O) and heavy water (D2O) conditions. In the temperature range of 150-550 C in a wet gas atmosphere the conductivity is significantly higher than that observed for dry conditions, indicating that protons are the dominant charge carriers. Conductivity is also found to be higher in dry oxygen in comparison with dry argon over the whole temperature range of 150-1000 C, characteristic of contribution from p-type charge carriers under oxidising atmospheres. At 550 C the proton conductivity was estimated to be 2.89 × 10- 4 S cm- 1 in wet Ar. Fitting of conductivity data provides a hydration enthalpy change (ΔH hydr 0) of - 100 ± 5 kJ/mol and hydration entropy change (ΔShydr 0) of - 160 ± 10 J/mol K.
41.	Rahman, Seikh Mohammad Habibur, 1976, et al. (författare) Synthesis and Enhanced Proton Conduction in a 20 mol% Ytterbium Doped Barium Zirconate Ceramic Using Zn as Sintering Aid 2012 Ingår i: Applied Mechanics and Materials. - 1660-9336 .- 1662-7482. - 9783037852620 ; 110-116:Part 1-7, s. 1181-1186 Konferensbidrag (refereegranskat)abstract 20% Ytterbium(III)-doped perovskite structured barium zirconate, BaZrO3, was prepared by two different synthesis routes: solid state and sol-gel routes. 2 % Zinc(II) was added as an acceptor dopant at the Zr(IV) site according to stoichiometry. It was also added as 2 % excess of the formula. The purpose of this study is to see how zinc(II) acts as a sintering aid in view of synthesis route, densification and conductivity of the material. A dense ceramic (90% of theoretical density) was achieved by the sol-gel method when stoichiometry was adjusted. Phase purity of the samples was checked by X-ray powder diffraction (XRD). Thermogravimetric analysis (TGA) and Impedance spectroscopy (IS) was used to characterize hydration and electrical conductivity respectively. The data shows that the addition of stoichiometric amounts of Zn2+ via sol-gel synthesis route promotes not only densification but also water incorporation and conductivity in comparison with the solid state route, keeping the same final sintering temperature of 1500 degrees C. For example, pre-hydrated BaZr0.78Zn0.02Yb0.2O3-delta, prepared via the sol-gel method shows total conductivity (sigma(tot)) value of 3.1410(-5) and 3.8 10(-3) Scm(-1), whereas for the solid state route, sigma(tot) values are 1.7410(-5) and 8.8710(-4) Scm(-1) under dry Ar (heating cycle) at 300 degrees C and 600 degrees C, respectively.

Skapa referenser, mejla, bekava och länka

Länka till träfflistan

Träfflista för sökning "WFRF:(Ahmed Istaq 1972) "

Avgränsa träffmängd

År