| 1. |
- Brant, William R., et al.
(författare)
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Local structure transformations promoting high lithium diffusion in defect perovskite type structures
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 441
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Sharma, Pratigya, et al.
(författare)
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Zn Metal Atom Doping on the Surface Plane of One-Dimesional NiMoO4 Nanorods with Improved Redox Chemistry
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:40, s. 44815-44829
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Tidskriftsartikel (refereegranskat)abstract
- The effect of zinc (Zn) doping and defect formation on the surface of nickel molybdate (NiMoO4) structures with varying Zn content has been studied to produce one-dimensional electrodes and catalysts for electrochemical energy storage and ethanol oxidation, respectively. Zn-doped nickel molybdate (Ni1-xZnxMoO4, where x = 0.1, 0.2, 0.4, and 0.6) nanorods were synthesized by a simple wet chemical route. The optimal amount of Zn is found to be around 0.25 above which the NiMoO4 becomes unstable, resulting in poor electrochemical activity. This result agrees with our density functional theory calculations in which the thermodynamic stability reveals that Ni1-xZnxMoO4 crystallized in the beta-NiMoO4 phase and is found to be stable for x=0.25. Analytical techniques show direct evidence of the presence of Zn in the NiMoO4 nanorods, which subtly alter the electrocatalytic activity. Compared with pristine NiMoO4, Zn-doped NiMoO4 with the optimized Zn content was tested as an electrode for an asymmetric supercapacitor and demonstrated an enhanced specific capacitance of 122 F g(-1) with a high specific energy density of 43 W h kg(-1) at a high power density of 384 W kg(-1). Our calculations suggest that the good conductivity from Zn doping is attributed to the formation of excess oxygen vacancies and dopants play an important role in enhancing the charge transfer between the surface and OH ions from the electrolyte. We report electrochemical testing, material characterization, and computational insights and demonstrate that the appropriate amount of Zn in NiMoO4 can improve the storage capacity (similar to 15%) due to oxygen vacancy interactions.
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| 3. |
- Yamada, Tsunetomo, et al.
(författare)
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Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal
- 2016
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Ingår i: IUCrJ. - 2052-2525. ; 3, s. 247-258, s. 95-
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Tidskriftsartikel (refereegranskat)abstract
- The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.
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| 4. |
- Yamada, Tsunetomo, et al.
(författare)
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Atomic structures of the Sc-Zn and R-Cd icosahedral quasicrystals
- 2017
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Ingår i: Acta Crystallographica Section A. - 2053-2733. ; A73:Suppl., s. C1317-C1317
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Tidskriftsartikel (refereegranskat)abstract
- We present the refinement results of atomic structures of binary icosahedral (i) ScZn7.3, GdCd7.9, DyCd7.5 and TmCd7.3 quasicrystals (QCs) [1, 2] and the study of phason modes. Bragg peak intensities data collection has been carried out on the CRISTAL beamline at the synchrotron SOLEIL, using an incoming X-ray energies equal to 25.5 keV (Sc-Zn) and 24.2 keV (R-Cd), and a CCD camera located at 8 cm from the samples. For all iQC samples a high redundancy (average 50) has been obtained resulting in 4057 (Sc-Zn) and 4871 ~ 5130 (R-Cd) unique reflections having intensity larger than 3 sigma and internal R factors around 8 %. The atomic structures of the iQCs were solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one [3] and the refinement program named qcdiff by A. Yamamoto, resulting in R factors equal to 10.9 % (Sc-Zn) and 8.9 ~ 10.9 % (R-Cd). The resulting structures are described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters (RTH) and double Friauf polyhedra (DFP), both resulting from a close-packing of large (Sc, R) and small (Zn, Cd) atoms. The significant difference in alloy composition between i-ScZn7.3, i-RCd~7.9 and the ideal model of i-YbCd5.7 was found to lay mainly on the DFP where one of the two large atom site (Sc, R) is replaced by a small atom (Zn, Cd) resulting in a significant distortion of the DFP. Residual disorder with relative occupancies of Sc(R)/Zn(Cd)=80/20 was also found on the icosahedral site. This illustrates that a detailed understanding of the atomic structure can now be achieved in QCs. The stabilization mechanism for these binary iQCs and the microscopic origins to explain the phason fluctuations will be discussed in this presentation. (1) Canfield, P. C., Caudle, M. L., Ho, C. S., Kreyssig, A., Nandi, S., Kim, M. G., Lin, X., Kracher, A., Dennis, K. W., McCallum, R. W. & Goldman, A. I. (2010) Phys. Rev. B, Solution growth of a binary icosahedral quasicrystal of Sc12Zn88, 81, 020201. (2) Goldman, A. I., Kong, T., Kreyssig, A., Jesche, A., Ramazanoglu, M., Dennis, K. W., et al. (2013). Nature Materials, A family of binary magnetic icosahedral quasicrystals based on rare earths and cadmium, 12(8), 714–718. (3) Takakura, H., Gómez, C. P., Yamamoto, A., de Boissieu, M., & Tsai, A. P. (2006). Nature Materials, Atomic structure of the binary icosahedral Yb–Cd quasicrystal, 6(1), 58–63.
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| 5. |
- Yamada, Tsunetomo, et al.
(författare)
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Diffuse scattering and phason modes in the Zn-Sc icosahedral quasicrystal
- 2012
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Konferensbidrag (refereegranskat)abstract
- Recently, a new binary icosahedral quasicrystal Zn-Sc has been obtained by Canfield et. al. [1]. Because of the chemical order and the x-ray contrast between Zn and Sc, this phase is a nice system for the structure refinement. On the other hand, a large amount of diffuse scattering can be seen on the x-ray diffraction pattern [1]. In this study, we carried out an absolute scale measurement of the x-ray diffuse scattering of i-ZnSc to study the possible presence of phason modes (phason diffuse scattering) and estimate phason elastic constats K1 and K2. Millimeter size single grain of i-ZnSc was obtained by slowly cooling from the melt. Systematic Q-scans and diffuse scattering maps have been measured on the D2AM beamline (ESRF) using an incoming x-ray energy equal to 9.3 keV. Compared with i-ZnMgSc quasicrystal [2], we find that the amount of diffuse scattering is larger in i-ZnSc sample. Also, the maximal Qperp value necessary for indexing the diffraction pattern was found to be less than 3 (r.l.u.) i.e. much smaller than for i-ZnMgSc for which it was found to be 7 [2]. In addition, as for other quasicrystals [3] a characteristic diffuse intensity distribution due to phason fluctuations around strong Bragg reflections is clearly visible on the systematic reciprocal space map. The ratio K2/K1 is found to be close to the three-fold instability limit, which results in the strong elongation of the diffuse scattering along directions parallel to a three-fold axis. Finally, the simulation is carried out based on the elastic theory and reproduces well the observed anisotropic shape of the diffuse scattering. [1] P. C. Canfield, et. al., Phys. Rev. B, 2010, 81, 020201. [2] M. de Boissieu, et. al., Phys. Rev. Lett., 2005, 95, 105503. [3] T. Janssen, et. al., Aperiodic Crystals. Oxford University Press, 2007
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| 6. |
- Yamada, Tsunetomo, et al.
(författare)
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Diffuse Scattering in the Zn6Sc 1/1 cubic approximant.
- 2010
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Konferensbidrag (refereegranskat)abstract
- The low-temperature phase transition of the Zn6Sc cubic 1/1 approximant [1] has been investigated by X-ray diffraction. It is a crystalline approximant to a recently discovered quasicrystal Zn88Sc12 [2] and has a bcc lattice composed of a Tsai-type cluster with an orientationally disordered Zn tetrahedra at the centers [3]. The phase transition undergoes below 160K and has been attributed to the orientational ordering of the Zn tetrahedra along [110] direction of hightemperature phase [1, 4]. In order to obtain an insight into the orientational ordering occurring at the phase transition, diffuse scattering has been measured. Well above the phase transition at 220K (i.e. 60 K above) we observed a broad diffuse scattering intensity which sharpen and merges into a Bragg peak as the temperature decreases and reaches the transition temperature (Tc). This signature of short-range ordering above Tc will be discussed in details and compared to refined average structures obtained between Tc and room temperature by measuring Bragg peaks. [1] R. Tamura et al., Phys. Rev. B 71, 092203, (2005). [2] P. C. Canfield et al., Phy. Rev. B 81, 020201(R) (2010). [3] Q. Lin and J. D. Corbett, Inorg. Chem., 43, 1912, (2004). [4] T. Ishimasa et al., Phil. Mag., 87, 2887, (2007).
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| 7. |
- Yamada, Tsunetomo, et al.
(författare)
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Short- and long-range ordering during the phase transition of the Zn6Sc 1/1 cubic approximant
- 2013
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:20, s. 205405-
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Tidskriftsartikel (refereegranskat)abstract
- Using in situ x-ray scattering and synchrotron radiation, we have experimentally elucidated the mechanism of the cubic to monoclinic phase transition in the Zn6Sc 1/1 approximant to an icosahedral quasicrystal. The high-temperature cubic phase is described as a bcc packing of a large Tsai-type icosahedral cluster whose center is occupied by an orientationally disordered Zn-4 tetrahedron. A clear monoclinic distortion has been found to take place within 2 K around T-c = 157 K, in excellent agreement with the observed anomalies in the electrical resistivity and heat capacity. Also, a rapid variation of the super-structure reflection intensity is observed. The low-temperature monoclinic phase, as determined by single-crystal x-ray diffraction at 40 K, has been confirmed to consist of ordered Zn-4 tetrahedra, oriented in an anti-parallel way along the [(1) over bar 01] direction. Above T-c, a diffuse scattering signal is observed at the position of the super-structure reflections, which evidences that a short-range ordering of the Zn-4 tetrahedra takes place. In a way similar to a second-order phase transition, the correlation length describing this short-range ordering increases rapidly when the temperature diminishes and almost diverges when the temperature is close to T-c, going from 200 angstrom at 220 K to reach the very large value of 1200 angstrom at 161 K. Finally, using single-crystal x-ray diffraction, the atomic structure of the low-temperature monoclinic super-structure (space group C2/c) could be solved. The ordering of the Zn-4 tetrahedra is accompanied by a strong distortion of the surrounding shells.
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