| 1. |
- Andersson, Matilda, et al.
(författare)
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Deposition and characterization of magnetron sputtered amorphous Cr-C films
- 2012
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 86:9, s. 1408-1416
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Tidskriftsartikel (refereegranskat)abstract
- Thin films in the Cr-C system with carbon content of 25-85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 degrees C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrCx phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young's modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp(2)/sp(3) ratio of the a-C phase.
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| 2. |
- Andersson, Matilda, et al.
(författare)
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Magnetron sputtering of Zr-Si-C thin films
- 2012
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 520:20, s. 6375-6381
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Tidskriftsartikel (refereegranskat)abstract
- The phase composition and chemical bonding of Zr-C and Zr-Si-C films deposited by magnetron sputtering has been studied. The results show that the binary Zr-C films at higher carbon contents form nanocrystallites of ZrC in an amorphous carbon matrix. The addition of Si induces a complete amorphization of the films above a critical concentration of about 15 at.%. X-ray diffraction and transmission electron microscopy confirm that the amorphous films contain no nanocrystallites and therefore can be described as truly amorphous carbides. The amorphous films are thermally stable but start to crystallize above 500 degrees C. Analysis of the chemical bonding with X-ray photoelectron spectroscopy suggests that the amorphous films exhibit a mixture of different chemical bonds such as Zr-C, Zr-Si and Si-C and that the electrical and mechanical properties are dependent on the distribution of these bonds. For higher carbon contents, strong Si-C bonds are formed in the amorphous Zr-Si-C films making them harder than the corresponding binary Zr-C films.
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| 3. |
- Dahbi, Mohammed, et al.
(författare)
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Combustion synthesis and electrochemical performance of Li2FeSiO4/C cathode material for lithium-ion batteries
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 205, s. 456-462
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Tidskriftsartikel (refereegranskat)abstract
- A novel preparation technique was developed for synthesizing Li2FeSiO4/C nanoparticles through combustion of reaction mixtures containing silicon source. Li and Fe sources that operate as oxidizers and sucrose that act as a fuel. A systematic investigation of the synthesis parameters, such as the effect of the fuel content, on purity, morphology and electrochemical properties of the samples was performed. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) and electrochemical measurements, respectively. Among the synthesized cathode materials, Li2FeSiO4 obtained with 1.5 mol of sucrose, showed the best electrochemical performance in terms of discharge capacity, cycling stability and rate capability. Discharge capacity of 130 mAh/g at C/20, 88 mAh/g at C/2 and 44 mAh/g at 2C were obtained with no capacity fading after 50 cycles.
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| 4. |
- Kadas, Krisztina, et al.
(författare)
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Structural properties of amorphous metal carbides : Theory and experiment
- 2012
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:12, s. 4720-4728
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Tidskriftsartikel (refereegranskat)abstract
- By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected: Zr0.31Si0.29C0.40 and Zr0.60Si0.33C0.07. Amorphous structures are generated in the theoretical part of our work by the stochastic quenching (SQ) method, and detailed comparison is made regarding the structure and density of the experimentally synthesized films. These films are analyzed experimentally using X-ray absorption spectroscopy, transmission electron microscopy and X-ray diffraction. Our results demonstrate a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.
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| 5. |
- Younesi, Reza, et al.
(författare)
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The Cathode Surface Composition of a Cycled Li–O2 Battery : A Photoelectron Spectroscopy Study
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:39, s. 20673-20680
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Tidskriftsartikel (refereegranskat)abstract
- A layer of reaction products, dominantly built up of C and O in the form of ethers and lithium alkyl carbonates, is formed on the surface of the carbon cathode during discharge of a Li–O2 battery in an electrolyte of 1 M LiPF6 in PC. The results are based on a detailed surface analysis combining the use of in house X-ray photoelectron spectroscopy (XPS) and synchrotron based hard X-ray photoelectron spectroscopy (HAXPES). The Li–O2 batteries were investigated at uncycled state (stored), after the first discharge, after the first charge, and at the end of life (discharge state). The results showed little to no Li2O2 and/or Li2O among the discharge products. The surface layers on the cathode were dominantly removed during charging of the battery. At the end of battery life, no complete discharge product layer is formed. The cathodes showed a strong indication of binder decomposition during cycling of the Li–O2 cell. Overall, the results obtained in this investigation show that the whole cathode formulation as well as the electrolyte composition need a completely new approach for the realization of a recyclable Li–O2 battery.
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