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Kaplan, M., Srinath, A., Riekehr, L., Nyholm, L., Hjörvarsson, B. & Fritze, S. (2022). Combinatorial design of amorphous TaNiSiC thin films with enhanced hardness, thermal stability, and corrosion resistance. Materials & design, 220, Article ID 110827.
Open this publication in new window or tab >>Combinatorial design of amorphous TaNiSiC thin films with enhanced hardness, thermal stability, and corrosion resistance
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2022 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 220, article id 110827Article in journal (Refereed) Published
Abstract [en]

Amorphous TaNiSiC and TaNiC films (with varying Ta/Ni and Si/C ratios) were deposited using combinatorial magnetron sputtering. The TaNiSiC films remained X-ray amorphous after four hour-long annealings up to 700 °C, while TaNiC alloys with high Ni and C contents crystallized. These differences were attributed to a strong driving force for separation of Ni and C in TaNiC, whereas the addition of Si, due to its solubility in the other elements, reduced the elemental segregation in TaNiSiC. The as-deposited TaNiSiC films exhibited hardnesses of 9–12 GPa. Annealing led to an increase in hardness by 2–4 GPa, due to decreases in average atomic distance, as evidenced by X-ray diffraction measurements. Potentiodynamic polarizations from –0.7 to +1.5 V vs. Ag/AgCl (3 M NaCl) in 10 mM sodium borate showed lower current densities by up to 2 orders of magnitude with increasing Ta content (28–52 at.%). Changes in Si/C content (7–13 at.% Si) had no effect. However, optical microscopy showed that TaNiSiC films with high Si/low C contents (13/10 at.%) suffered much less localized etching compared to TaNiC films. Thus, Si had a significant role in increasing the mechanical strength, corrosion resistance, and thermal stability of the TaNiSiC films.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Metal lic glasses, thermal stability, mechanical properties, corrosion resis- tance
National Category
Materials Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-468121 (URN)10.1016/j.matdes.2022.110827 (DOI)000826404700006 ()
Funder
Swedish Foundation for Strategic Research, GMT14-0048Swedish Research CouncilSwedish Research Council
Available from: 2022-02-20 Created: 2022-02-20 Last updated: 2022-08-12Bibliographically approved
Osinger, B., Mao, H., Fritze, S., Riekehr, L., Jansson, U. & Lewin, E. (2022). Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings. Materials & design, 221, Article ID 111002.
Open this publication in new window or tab >>Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings
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2022 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 221, article id 111002Article in journal (Refereed) Published
Abstract [en]

Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase forma-tion, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were inves-tigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 degrees C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 degrees C exhibited a single NaCl-type multicom-ponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 degrees C, or exposed to UHV annealing at 1000 degrees C, however, revealed the decom-position of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in appli-cations at elevated temperatures.

Place, publisher, year, edition, pages
ElsevierElsevier BV, 2022
Keywords
High entropy ceramics, Multi -principal element carbide, Multicomponent carbide, Physical vapour deposition (PVD), CALPHAD
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-482676 (URN)10.1016/j.matdes.2022.111002 (DOI)000839257000004 ()
Funder
Swedish Research Council, 2018-04834Swedish Research CouncilSwedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research, RIF14-0053
Available from: 2022-09-07 Created: 2022-09-07 Last updated: 2024-01-15Bibliographically approved
Karlsson, D., Beran, P., Riekehr, L., Tseng, J.-C., Harlin, P., Jansson, U. & Cedervall, J. (2022). Structure and Phase Transformations in Gas Atomized AlCoCrFeNi High Entropy Alloy Powders. Journal of Alloys and Compounds, 893, Article ID 162060.
Open this publication in new window or tab >>Structure and Phase Transformations in Gas Atomized AlCoCrFeNi High Entropy Alloy Powders
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2022 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 893, article id 162060Article in journal (Refereed) Published
Abstract [en]

In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (½ ½ ½) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and σ phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of σ phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys.

Place, publisher, year, edition, pages
ElsevierElsevier BV, 2022
National Category
Metallurgy and Metallic Materials Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-451657 (URN)10.1016/j.jallcom.2021.162060 (DOI)000714750200004 ()
Funder
Swedish Foundation for Strategic Research, GMT14-004 8Swedish Research Council
Available from: 2021-08-28 Created: 2021-08-28 Last updated: 2024-01-15Bibliographically approved
Zendejas Medina, L., Tavares da Costa, M. V., Paschalidou, E. M., Lindwall, G., Riekehr, L., Korvela, M., . . . Jansson, U. (2021). Enhancing corrosion resistance, hardness, and crack resistance in magnetron sputtered high entropy CoCrFeMnNi coatings by adding carbon. Materials & design, 205, Article ID 109711.
Open this publication in new window or tab >>Enhancing corrosion resistance, hardness, and crack resistance in magnetron sputtered high entropy CoCrFeMnNi coatings by adding carbon
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2021 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 205, article id 109711Article in journal (Refereed) Published
Abstract [en]

This study explores carbon addition as a materials design approach for simultaneously improving the hardness, crack resistance, and corrosion resistance of high entropy thin films. CoCrFeMnNi was selected as a starting point, due to its high concentration of weak carbide formers. The suppression of carbides is crucial to the approach, as carbide formation can decrease both ductility and corrosion resistance. Films with 0, 6, and 11 at.% C were deposited by magnetron co-sputtering, using a graphite target and a sintered compound target. The samples with 0 at.% C crystallized with a mixture of a cubic closed packed (ccp) phase and the intermetallic χ-phase. With 6 and 11 at.% C, the films were amorphous and homogenous down to the nm-scale. The hardness of the films increased from 8 GPa in the carbon-free film to 16 GPa in the film with 11 at.% C. Furthermore, the carbon significantly improved the crack resistance as shown in fragmentation tests, where the crack density was strongly reduced. The changes in mechanical properties were primarily attributed to the shift from crystalline to amorphous. Lastly, the carbon improved the corrosion resistance by a progressive lowering of the corrosion current and the passive current with increasing carbon concentration.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Thin film, Magnetron sputtering, Corrosion, Fragmentation test, Amorphous alloys, Bipolar plate
National Category
Materials Chemistry Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-448906 (URN)10.1016/j.matdes.2021.109711 (DOI)000659520300002 ()
Funder
Swedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, 2018-04834Vinnova, 2016-05156
Available from: 2021-07-13 Created: 2021-07-13 Last updated: 2024-01-15Bibliographically approved
Gouillart, L., Cattoni, A., Chen, W.-C., Goffard, J., Riekehr, L., Keller, J., . . . Collin, S. (2021). Interface engineering of ultrathin Cu(In,Ga)Se2 solar cells on reflective back contacts. Progress in Photovoltaics, 29(2), 212-221
Open this publication in new window or tab >>Interface engineering of ultrathin Cu(In,Ga)Se2 solar cells on reflective back contacts
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2021 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 29, no 2, p. 212-221Article in journal (Refereed) Published
Abstract [en]

Cu(In,Ga)Se-2-based (CIGS) solar cells with ultrathin (<= 500 nm) absorber layers suffer from the low reflectivity of conventional Mo back contacts. Here, we design and investigate ohmic and reflective back contacts (RBC) made of multilayer stacks that are compatible with the direct deposition of CIGS at 500 degrees C and above. Diffusion mechanisms and reactions at each interface and in the CIGS layer are carefully analyzed by energy dispersive X-ray (EDX)/scanning transmission electron microscopy (STEM). It shows that the highly reflective silver mirror is efficiently encapsulated in ZnO:Al layers. The detrimental reaction between CIGS and the top In2O3:Sn (ITO) layer used for ohmic contact can be mitigated by adding a 3 nm thick Al2O3 layer and by decreasing the CIGS coevaporation temperature from 550 degrees C to 500 degrees C. It also improves the compositional grading of Ga toward the CIGS back interface, leading to increased open- circuit voltage and fill factor. The best ultrathin CIGS solar cell on RBC exhibits an efficiency of 13.5% (+1.0% as compared to our Mo reference) with a short-circuit current density of 28.9 mA/cm(2) (+2.6 mA/cm(2)) enabled by double-pass absorption in the 510 nm thick CIGS absorber. RBC are easy to fabricate and could benefit other photovoltaic devices that require highly reflective and conductive contacts subject to high temperature processes.

Place, publisher, year, edition, pages
John Wiley & SonsWiley, 2021
Keywords
CIGS, interface engineering, reflective back contact, silver, ultrathin solar cells
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-438836 (URN)10.1002/pip.3359 (DOI)000591710600001 ()
Funder
EU, Horizon 2020, 720887
Available from: 2021-04-06 Created: 2021-04-06 Last updated: 2024-01-15Bibliographically approved
Fritze, S., Chen, M., Riekehr, L., Osinger, B., Sortica, M. A., Srinath, A., . . . Jansson, U. (2021). Magnetron sputtering of carbon supersaturated tungsten films-A chemical approach to increase strength. Materials & design, 208, Article ID 109874.
Open this publication in new window or tab >>Magnetron sputtering of carbon supersaturated tungsten films-A chemical approach to increase strength
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2021 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 208, article id 109874Article in journal (Refereed) Published
Abstract [en]

Tungsten (W)-based materials attract significant attention due to their superior mechanical properties. Here, we present a chemical approach based on the addition of carbon (C) for increased strength via the combination of three strengthening mechanisms in W thin films. W:C thin films with C concentrations up to-4 at.% were deposited by magnetron sputtering. All films exhibit a body-centred-cubic structure with strong texture and columnar growth behaviour. X-ray and electron diffraction measurements suggest the formation of supersaturated W:C solid solution phases. The addition of C reduced the average column width from-133 nm for W to-20 nm for the film containing-4 at.% C. The column refinement is explained by a mechanism where C acts as re-nucleation sites. The W film is-13 GPa hard, while the W:C films achieve a peak hardness of-24 GPa. The W:C films are-11 GPa harder than the W film, which is explained by a combination of grain refinement strengthening, solid solution strengthening and increased dislocation density. Additional micropillar compression tests showed that the flow stress increased upon C addition, from-3.8 to-8.3 GPa and no brittle fracture was observed.

Place, publisher, year, edition, pages
ElsevierElsevier BV, 2021
Keywords
Small-scale mechanical characterisation, Tungsten, PVD, Supersaturated solid solution
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-453476 (URN)10.1016/j.matdes.2021.109874 (DOI)000684858300005 ()
Funder
Swedish Research Council, 201804834Swedish Foundation for Strategic Research Swedish Research CouncilSwedish Research Council, 82120125144Swedish Research Council, 201700646_9Swedish Foundation for Strategic Research , RIF140053
Available from: 2021-09-23 Created: 2021-09-23 Last updated: 2024-01-15Bibliographically approved
Naim Katea, S., Riekehr, L. & Westin, G. (2021). Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite. Journal of the European Ceramic Society, 41(1), 62-72
Open this publication in new window or tab >>Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite
2021 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 41, no 1, p. 62-72Article in journal (Refereed) Published
Abstract [en]

Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO2 and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin−1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar+-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO2 was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
ZrC, Nano-phase powder, Carbothermal reduction, Sol-gel, Core-shell particle
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-420940 (URN)10.1016/j.jeurceramsoc.2020.03.055 (DOI)000582675600005 ()
Available from: 2020-10-02 Created: 2020-10-02 Last updated: 2024-01-15Bibliographically approved
Menon, A. S., Ulusoy, S., Ojwang, D. O., Riekehr, L., Didier, C., Peterson, V. K., . . . Brant, W. (2021). Synthetic Pathway Determines the Nonequilibrium Crystallography of Li- and Mn-Rich Layered Oxide Cathode Materials. ACS Applied Energy Materials, 4(2), 1924-1935
Open this publication in new window or tab >>Synthetic Pathway Determines the Nonequilibrium Crystallography of Li- and Mn-Rich Layered Oxide Cathode Materials
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2021 (English)In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 4, no 2, p. 1924-1935Article in journal (Refereed) Published
Abstract [en]

Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol-gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.

Place, publisher, year, edition, pages
American Chemical Society (ACS)AMER CHEMICAL SOC, 2021
Keywords
Li- and Mn-rich layered oxides, Li-ion battery cathodes, synthesis-structure relationships, anionic redox materials, stacking faulted materials
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-440091 (URN)10.1021/acsaem.0c03027 (DOI)000621660800092 ()
Funder
Swedish Foundation for Strategic Research StandUpSwedish Energy AgencySwedish Research Council, 349-2014-3946Swedish Research Council, 2016-06959
Available from: 2021-04-16 Created: 2021-04-16 Last updated: 2024-04-24Bibliographically approved
Jacobsson, T. J., Hultqvist, A., Svanström, S., Riekehr, L., Cappel, U. B., Unger, E., . . . Boschloo, G. (2020). 2-Terminal CIGS-perovskite tandem cells: A layer by layer exploration. Solar Energy, 207, 270-288
Open this publication in new window or tab >>2-Terminal CIGS-perovskite tandem cells: A layer by layer exploration
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2020 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 207, p. 270-288Article in journal (Refereed) Published
Abstract [en]

This paper focuses on the development of 2-terminal CIGS-perovskite tandem solar cells by exploring a range of stack sequences and synthetic procedures for depositing the associated layers. In the end, we converged at a stack sequence composed of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al/NiO/PTAA/Perovskite/LiF/PCBM/SnO2/ITO. With this architecture, we reached performances only about 1% lower than the corresponding 4-terminal tandem cells, thus demonstrating functional interconnects between the two sub-cells while grown monolithically on top of each other. We go through the stack, layer-by-layer, discussing their deposition and the results, from which we can conclude what works, what does not work, and what potentially could work after additional modifications. The challenges for a successful 2-terminal tandem device include: how to deal with, or decrease, the surface roughness of the CIGS-stack, how to obtain uniform coverage of the layers between the CIGS and the perovskite while also obtaining a benign interface chemistry, and how to tune the band gaps of both the CIGS and the perovskite to obtain good optical matching. The investigation was based on CIGS with a power conversion efficiency around 14%, and perovskites with an efficiency around 12%, resulting in 2-terminal tandem cells with efficiencies of 15–16%. The results indicate that by using higher performing CIGS and perovskite sub-cells, it should be possible to manufacture highly efficient 2-terminal CIGS-perovskite tandem devices by using the protocols, principles, and procedures developed and discussed in this paper.

Keywords
Perovskite, CIGS, Tandem, 2-terminal, Solar cell
National Category
Materials Chemistry Other Electrical Engineering, Electronic Engineering, Information Engineering Energy Engineering
Identifiers
urn:nbn:se:uu:diva-427767 (URN)10.1016/j.solener.2020.06.034 (DOI)000575902500010 ()
Funder
Swedish Energy Agency, 43549-1Swedish Foundation for Strategic Research, RMA15-0130StandUp
Available from: 2020-12-11 Created: 2020-12-11 Last updated: 2024-06-04Bibliographically approved
Comparotto, C., Davydova, A., Ericson, T., Riekehr, L., Moro, M. V., Kubart, T. & Scragg, J. J. (2020). Chalcogenide Perovskite BaZrS3: Thin Film Growth by Sputtering and Rapid Thermal Processing. ACS Applied Energy Materials, 3(3), 2762-2770
Open this publication in new window or tab >>Chalcogenide Perovskite BaZrS3: Thin Film Growth by Sputtering and Rapid Thermal Processing
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2020 (English)In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 3, no 3, p. 2762-2770Article in journal (Refereed) Published
Abstract [en]

Tandem solar cells based on hybrid organic-inorganic metal halide perovskites have reached efficiencies up to 28%, but major concerns for long-term stability and the presence of Pb have raised interest in searching for fully earth-abundant, intrinsic chemically stable, and nontoxic alternatives. With a direct band gap around 1.8 eV and stability in air up to at least 500 degrees C, BaZrS3 is a promising candidate. This work presents the first approach of synthesizing a thin film of such compound by sputtering at ambient temperature with a subsequent rapid thermal process. Despite the short fabrication time, the width of the XRD diffraction peaks and the energy and distribution of the photoluminescence response show comparable crystalline quality to that from bulk synthesis methods. Good crystallization required around 900 degrees C. Such a high temperature could be incompatible with fabrication of tandem solar cells.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2020
Keywords
chalcogenides, perovskites, sputtering, photovoltaics, tandem solar cells
National Category
Materials Chemistry Condensed Matter Physics Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-411307 (URN)10.1021/acsaem.9b02428 (DOI)000526598300077 ()
Funder
Swedish Research Council, 2017-04336Swedish Foundation for Strategic Research , RIF14-0053StandUpSwedish Research Council, 821-2012-5144Swedish Research Council, 2017-00646_9Swedish Research Council, 2018-04834Göran Gustafsson Foundation for Research in Natural Sciences and Medicine, 1927
Available from: 2020-05-31 Created: 2020-05-31 Last updated: 2020-12-15Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1874-932x

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