| 1. |
- Brant, William, et al.
(author)
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Comparative analysis of ex-situ and operando X-ray diffraction experiments for lithium insertion materials
- 2016
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 302, s. 126-134
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Journal article (peer-reviewed)abstract
- AbstractA comparative study of ex-situ and operando X-ray diffraction techniques using the fast lithium ion conductor Li0.18Sr0.66Ti0.5Nb0.5O3 is presented. Ex-situ analysis of synchrotron X-ray diffraction data suggests that a single phase material exists for all discharges to as low as 0.422 V. For samples discharged to 1 V or lower, i.e. with higher lithium content, it is possible to determine the lithium position from the X-ray data. However, operando X-ray diffraction from a coin cell reveals that a kinetically driven two phase region occurs during battery cycling below 1 V. Through monitoring the change in unit cell dimension during electrochemical cycling the dynamics of lithium insertion are explored. A reduction in the rate of unit cell expansion of 22(2)% part way through the first discharge and 13(1)% during the second discharge is observed. This reduction may be caused by a drop in lithium diffusion into the bulk material for higher lithium contents. A more significant change is a jump in the unit cell expansion by 60(2)% once the lithium content exceeds one lithium ion per vacant site. It is suggested that this jump is caused by damping of octahedral rotations, thus establishing a link between lithium content and octahedral rotations.Graphical abstract
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| 2. |
- Brant, William R, et al.
(author)
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A large format in operando wound cell for analysing the structural dynamics of lithium insertion materials
- 2016
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 336, s. 279-285
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Journal article (peer-reviewed)abstract
- This paper presents a large wound cell for in operando neutron diffraction (ND) from which high quality diffraction patterns are collected every 15 min while maintaining conventional electrochemical performance. Under in operando data collection conditions the oxygen atomic displacement parameters (ADPs) and cell parameters were extracted for Li0.18Sr0.66Ti0.5Nb0.5O3. Analysis of diffraction data collected under in situ conditions revealed that the lithium is located on the (0.5 0.5 0) site, corresponding to the 3c Wyckoff position in the cubic perovskite unit cell, after the cell is discharged to I V. When the cell is discharged under potentiostatic conditions the quantity of lithium on this site increases, indicating a potential position where lithium becomes pinned in the thermodynamically stable phase. During this potentiostatic step the oxygen ADPs reduce significantly. On discharge, however, the oxygen ADPs were observed to increase gradually as more lithium is inserted into the structure. Finally, the rate of unit cell expansion changed by similar to 44% once the lithium content approached similar to 0.17 Li per formula unit. A link between lithium content and degree of mobility, disorder of the oxygen positions and changing rate of unit cell expansion at various stages during lithium insertion and extraction is thus presented.
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| 3. |
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| 4. |
- Brant, William R., et al.
(author)
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Local structure transformations promoting high lithium diffusion in defect perovskite type structures
- 2023
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 441
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Journal article (peer-reviewed)abstract
- Defect perovskites, AxBO3 such as (Li3xLa2/3-x)TiO3, are attracting attention as high capacity electrodes in lithium-ion batteries. However, the mechanism enabling high lithium storage capacities has not been fully investigated. In this work, the reversible insertion and removal of lithium up to an average A-site cavity occupancy of 1.71 in the defect perovskite (Li0.18Sr0.66)(Ti0.5Nb0.5)O3 is investigated. It was shown that subtle lithium reorganization during lithiation has a significant impact on enabling high capacity. Contrary to previous studies, lithium was coordinated to triangular faces of Ti/Nb oxygen octahedra and offset from O4 windows between A-site cavities in the as-synthesised material. Upon electrochemical lithiation Li-Li repulsion redistributes of all the lithium towards the O4 window position resulting in a loss of lithium mobility. Surprisingly, the mobility is regained during over-lithiation and following multiple electrochemical cycles. It is suggested that lithium reorganisation into the center of the O4 window alleviates the Li-Li repulsion and modifies the diffusion behavior from site percolation to bond percolation. The results obtained provide valuable insight into the chemical drivers enabling higher capacities and enhanced diffusion in defect perovskites. More broadly the study delivers fundamental understanding on the non-equilibrium structural transformations occurring within electrode materials during repeated electrochemical cycles.
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| 5. |
- Brant, William R., et al.
(author)
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Rapid Lithium Insertion and Location of Mobile Lithium in the Defect Perovskite Li0.18Sr0.66Ti0.5Nb0.5O3
- 2012
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In: ChemPhysChem. - : Wiley-Blackwell. - 1439-4235 .- 1439-7641. ; 13:9, s. 2293-2296
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Journal article (peer-reviewed)abstract
- Fast and fancy: Lithium that was originally disordered within the structure of the perovskite Li0.18Sr0.66Ti0.5Nb0.5O3 can be induced into ordering within the yellow region of the unit cell by low temperatures and treatment with n-butyl-lithium. The fast kinetics of lithium insertion, in connection with a color change, make this nontoxic, air-stable material a suitable candidate for use in electrochromic systems or lithium-storage batteries.
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| 6. |
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| 7. |
- Brant, William, et al.
(author)
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Selective Control of Composition in Prussian White for Enhanced Material Properties
- 2019
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In: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 31:18, s. 7203-7211
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Journal article (peer-reviewed)abstract
- Sodium-ion batteries based on Prussian blue analogues (PBAs) are ideal for large-scale energy storage applications due to the ability to meet the huge volumes and low costs required. For Na2-xFe[Fe(CN)(6)](1-y)center dot zH(2)O, realizing its commercial potential means fine control of the concentration of sodium, Fe(CN)(6) vacancies, and water content. To date, there is a huge variation in the literature of composition leading to variable electrochemical performance. In this work, we break down the synthesis of PBAs into three steps for controlling the sodium, vacancy, and water content via an inexpensive, scalable synthesis method. We produce rhombohedral Prussian white Na1.88(5)Fe[Fe-(CN)(6)]center dot 0.18(9)H2O with an initial capacity of 158 mAh/g retaining 90% capacity after 50 cycles. Subsequent characterization revealed that the increased polarization on the 3 V plateau is coincident with a phase transition and reduced utilization of the high-spin Fe(III)/Fe(II) redox couple. This reveals a clear target for subsequent improvements of the material to boost long-term cycling stability. These results will be of great interest for the myriad of applications of PBAs, such as catalysis, magnetism, electrochromics, and gas sorption.
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| 8. |
- Elmgren, Maja, 1964-, et al.
(author)
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Best Practices in the Use of Learning Outcomes in Chemistry Education
- 2013
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Conference paper (peer-reviewed)abstract
- Guiding chemistry education for the future requires the exchange of perspectives on core knowledge, skills and competencies. Learning outcomes-driven chemistry education is increasingly practiced, providing new opportunities for international comparisons. The interest in intended learning outcomes and constructive alignment has grown in many parts of the world due to both research in higher education [1] and political decisions (e. g. the Bologna process in Europe). We have developed a method for learning by sharing and comparing best practice of the use of these outcomes, to enhance learner-centered chemistry education both in the developed and developing countries. As a starting point, the overarching guidelines for chemistry education in Europe, North America and Australia were compared and discussed, with awareness of varying circumstances and terminology, which is necessary for this project to be useful in different settings. In focus were chemistry-specific and transferable skills as well as some higher order thinking skills (including aspects of conceptual, procedural and metacognitive knowledge [2]) rather than content and factual knowledge.The overarching guidelines were in turn compared with local learning outcomes for chemistry education at several universities. We evaluated how learning outcomes for courses and modules were linked to each other and to learning outcomes for educational programs. Furthermore we discussed how the expected learning outcomes were aligned with learning activities and assessment. A tool was designed to facilitate this, and used for self-analysis at the involved universities.We conclude that the method has promising features and can be used to elucidate the correspondence between learning outcomes at different levels, and the constructive alignment between learning outcomes, learning activities and assessment. A full electronic report and manual for the benchmarking procedure will be produced at the conclusion of the project, including a collection of examples of good/best practice for dissemination.ReferencesJ. B. Biggs and C. S. Tang, Teaching for quality learning at university: what the student does. (Open University Press, Maidenhead, 2011).L. W. Anderson and D. R. Krathwohl et al., Taxonomy for learning, teaching and assessing – A revision of Bloom’s taxonomy of educational objectives (Longman, New York, 2001)
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| 9. |
- Elmgren, Maja, et al.
(author)
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Comparison and Evaluation of Learning Outcomes from an International Perspective : Development of a Best-Practice Process
- 2015
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In: Journal of Chemical Education. - : American Chemical Society (ACS). - 0021-9584 .- 1938-1328. ; 92:3, s. 427-432
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Journal article (peer-reviewed)abstract
- Chemistry education focused on learning outcomes is increasingly practiced, providing new opportunities for international comparisons. The interest in intended learning outcomes and constructive alignment has grown in many parts of the world due to both research in higher education and political decisions. In an International Union of Pure and Applied Chemistry (IUPAC) project, we have developed a method of using critical evaluation of learning outcomes and descriptors at international, national, and institutional levels to enhance learner-centered chemistry education. This method is process-focused, aimed at learning by sharing and comparing practices around the world. Three overarching documents for the chemistry bachelor from the USA, Europe and Australia were compared. The differences were found to be more in style than in content. A tool for self-analysis was constructed to evaluate how learning outcomes for courses and modules are linked to each other and to learning outcomes for educational programs and how the expected learning outcomes can be aligned with learning activities and assessment. We conclude that the method can be used to elucidate the correspondence between learning outcomes at different levels, and the constructive alignment between learning outcomes, learning activities and assessment. The process gives new perspectives and shared knowledge. Chemistry education may need to be different depending on local considerations, and awareness of these differences is of value for further development.
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| 10. |
- Whittle, Thomas A., et al.
(author)
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Novel insight into the structure and properties of lead-free dielectric Sr3TiNb4O15
- 2018
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In: Journal of Materials Chemistry C. - : The Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 6:33, s. 8890-8896
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Journal article (peer-reviewed)abstract
- Sr3TiNb4O15 has been synthesised and its structure and dielectric properties characterised. In contrast to previously reported results the compound has been found to form with Pna21 symmetry and unit cell dimensions a = 12.3631(19), b = 12.4027(19) and c = 7.7601(12) Å. Variable temperature studies show a phase transition from orthorhombic to tetragonal symmetry at approximately 625 K, much higher than previously reported. Temperature-dependent dielectric measurements have also been performed and these correlate very well with the observed phase transition temperature.
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| 11. |
- Whittle, Thomas A., et al.
(author)
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Tailoring phase transition temperatures in perovskites via A-site vacancy generation
- 2017
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In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 46:22, s. 7253-7260
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Journal article (peer-reviewed)abstract
- The structures across the Sr0.8Ti0.6-xZrxNb0.4O3, 0 <= x <= 0.6, defect perovskite series were investigated using complementary synchrotron X-ray and neutron powder diffraction data. The locations of second order compositional and temperature dependent phase transitions between the high symmetry cubic Pm (3) over barm phase and the lower symmetry tetragonal I4/mcm phase were determined. Deviation of the oxygen x coordinate from the high symmetry value and the B-O-B bond angle from 180 degrees as well as the tetragonal strain squared were each found to be suitable order parameters to monitor the transitions. Tolerance factor calculations confirmed that these A-site deficient perovskites retain a higher symmetry to a lower value than their fully occupied counterparts. Therefore, adjusting vacancy concentrations can be employed as a general strategy to design compounds with specifically tailored phase transition temperatures.
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