| 1. |
- Xin, Tongzheng, et al.
(författare)
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Phase transformations in an ultralight BCC Mg alloy during anisothermal ageing
- 2022
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- Mg-Li-Al alloys with a body-centred cubic (BCC) structure can exhibit exceptional specific strengths in combination with excellent ductility and corrosion resistance. In general, the strength of these alloys is very sensitive to the processing temperature due to the occurrence of various phase transformations. Although different phases have been identified in these alloys, their corresponding transformation mechanisms and unique role played in controlling the mechanical properties have never been studied in depth. In this work, we identified the phase transformation sequence by in-situ synchrotron X-ray diffraction. Moreover, we investigated the evolution of precipitation and their morphology using transmission and scanning electron microscopy, together with simulations based on the phase field modelling and first-principles calculations. Phase transformation sequence of Al-rich zone?->?theta (D0(3)(-)Mg(3)Al)?->?AlLi was confirmed during anisothermal ageing. A braided structure resulting from spinodal decomposition was found to be the optimized microstructure for achieving the peak strength. Nanocrystalline alpha-Mg phase at the interface between theta and the matrix was identified as the main reason for softening in the alloy. The core-shell model for theta?->?AlLi transformation is observed and verified. Our findings deepen the understanding of BCC Mg-Li-Al alloys and pave a pathway to develop new generation of ultralight alloys with stronger strength and better stability. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 2. |
- Azina, Clio, et al.
(författare)
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Deposition of MAX phase-containing thin films from a (Ti,Zr)(2)AlC compound target
- 2021
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 551
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Tidskriftsartikel (refereegranskat)abstract
- This work reports on sputter depositions carried out from a compound (Ti,Zr)(2)AlC target on Al2O3(0 0 0 1) substrates at temperatures ranging between 500 and 900 degrees C. Short deposition times yielded 30-40 nm-thick Al-containing (Ti,Zr)C films, whereas longer depositions yielded thicker films up to 90 nm which contained (Ti,Zr)C and intermetallics. At 900 degrees C, the longer depositions led to films that also consisted of solid solution MAX phases. Detailed transmission electron microscopy showed that both (Ti,Zr)(2)AlC and (Ti,Zr)(3)AlC2 solid solution MAX phases were formed. Moreover, this work discusses the growth mechanism of the thicker films, which started with the formation of the mixed (Ti,Zr)C carbide, followed by the nucleation and growth of aluminides, eventually leading to solid state diffusion of Al within the carbide, at the highest temperature (900 degrees C) to form the MAX phases.
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| 3. |
- Lin, Zhipeng, et al.
(författare)
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Electrocatalyzed direct arene alkenylations without directing groups for selective late-stage drug diversification
- 2023
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Ingår i: Nature Communications. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemistry has emerged as an increasingly viable tool in molecular synthesis. Here the authors realize electrocatalyzed C-H activations, with the aid of data science and artificial intelligence, towards selective alkenylations for late-stage drug diversifications. Electrooxidation has emerged as an increasingly viable platform in molecular syntheses that can avoid stoichiometric chemical redox agents. Despite major progress in electrochemical C-H activations, these arene functionalizations generally require directing groups to enable the C-H activation. The installation and removal of these directing groups call for additional synthesis steps, which jeopardizes the inherent efficacy of the electrochemical C-H activation approach, leading to undesired waste with reduced step and atom economy. In sharp contrast, herein we present palladium-electrochemical C-H olefinations of simple arenes devoid of exogenous directing groups. The robust electrocatalysis protocol proved amenable to a wide range of both electron-rich and electron-deficient arenes under exceedingly mild reaction conditions, avoiding chemical oxidants. This study points to an interesting approach of two electrochemical transformations for the success of outstanding levels of position-selectivities in direct olefinations of electron-rich anisoles. A physical organic parameter-based machine learning model was developed to predict position-selectivity in electrochemical C-H olefinations. Furthermore, late-stage functionalizations set the stage for the direct C-H olefinations of structurally complex pharmaceutically relevant compounds, thereby avoiding protection and directing group manipulations.
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| 4. |
- Paul, Biplab, et al.
(författare)
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Effect of disordered nanoporosity on electrical and thermal properties of layered Ca3Co4O9 films
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:6
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Tidskriftsartikel (refereegranskat)abstract
- Independently controlling electronic and thermal transport in solids is a challenge, because these properties are coupled. Here, we show that disordered nanoporosity in Ca3Co4O9 thin films can decrease the thermal conductivity without significantly hampering electronic transport. Scanning thermal microscopy was used to determine the out-of-plane thermal conductivity and estimate the in-plane values. Nanoporous Ca3Co4O9 films exhibit a thermal conductivity of 0.82 W m(-1) K-1, which is nearly twofold lower than that obtained from nonporous Ca3Co4O9 films. Nanoporous Ca3Co4O9 exhibit a room-temperature electrical resistivity of 4 m omega cm, which is comparable to polycrystalline Ca3Co4O9 and twice that reported for single-crystal Ca3Co4O9. Our results suggest that controlling nanoporosity and their degree of disorder can offer a means of decoupling electrical and thermal properties in materials.
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| 5. |
- Shu, Rui, 1990-, et al.
(författare)
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Influence of Metal Substitution and Ion Energy on Microstructure Evolution of High-Entropy Nitride (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr) Films
- 2021
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Ingår i: ACS APPLIED ELECTRONIC MATERIALS. - : American Chemical Society (ACS). - 2637-6113. ; 3:6, s. 2748-2756
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr, 0.12 <= x <= 0.30) films were deposited on Si(100) substrates at 400 degrees C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from similar to 10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 <= x <= 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1-x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1-x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached similar to 3.1 GPa in Hf- and Cr-containing films deposited at -130 V. The hardness reached a maximum value of 28.0 +/- 1.0 GPa at a negative bias >= 100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1-x films can thus guide the design of protective high-entropy nitride films.
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| 6. |
- Wang, Lei, et al.
(författare)
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Mechanochemical Formation of Protein Nanofibril: Graphene Nanoplatelet Hybrids and Their Thermoelectric Properties
- 2020
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 8:47, s. 17368-17378
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Tidskriftsartikel (refereegranskat)abstract
- Hybrids between biopolymeric materials and low-cost conductive carbon-based materials are interesting materials for applications in electronics, potentially reducing the need for materials that generate environmentally harmful electronic waste. Herein we investigate a scalable ball-milling method to form graphene nanoplatelets (GNPs) by milling graphite flakes with aqueous dispersions of proteins or protein nanofibrils (PNFs). Aqueous GNP dispersions with high concentrations (up to 3.2 mg mL(-1)) are obtained under appropriate conditions. The PNFs/proteins help to exfoliate graphite and stabilize the resulting GNP dispersions by electrostatic repulsion. PNFs are prepared from hen egg white lysozyme (HEWL) and beta-lactoglobulin (BLG). The GNP dispersions can be processed into free-standing films having an electrical conductivity of up to 110 S m(-1). Alternatively, the GNP dispersions can be drop-cast on PET substrates, resulting in mechanically flexible films having an electrical conductivity of up to 65 S m(-1). The drop-cast films are investigated regarding their thermoelectric properties, having Seebeck coefficients of about 50 mu V K-1. By annealing drop-cast films and thus carbonizing residual PNFs, an increase of electrical conductivity, coupled with a modest decrease in Seebeck coefficient, is obtained resulting in materials displaying power factors of up to 4.6 mu W m(-1) K-2.
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| 7. |
- Xin, Binbin, et al.
(författare)
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Engineering Faceted Nanoporosity by Reactions in Thin-Film Oxide Multilayers in Crystallographically Layered Calcium Cobaltate for Thermoelectrics
- 2021
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:9, s. 9904-9911
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Tidskriftsartikel (refereegranskat)abstract
- Introducing porosity is attractive for tailoring electronic, thermal, and mechanical properties of inorganic materials. Nanoporosity is typically either inherent in crystallographic channels in the structure or obtained by external templating during synthesis and sintering. However, controllably engineering porosity in materials with laminated crystal structures without channels remains a challenge. Here, we demonstrate the realization of faceted and oriented nanopores in textured Ca3Co4O9-a laminated ceramic with a misfit-layered structure of importance for thermoelectric applications-from chemical reactions in CaO/Co3O4 multilayers. We show that CaO conversion to Ca(OH)(2) and the cobalt oxide stoichiometry are key determinants of nanoporosity. Adjusting the unreacted CaO fraction alters the nanopore size and fraction and the thermoelectric properties of Ca3Co4O9. The preferred orientation of Ca3Co4O9 is underpinned by the texture of the reactant multilayers and reactant-product crystallographic relationships and density difference. Oriented pore formation is attributed to basal plane removal driven by local densification of textured Ca3Co4O9 nuclei through growth and impingement. These findings point to possibilities for controllably engineering nanoporosity and properties in a variety of inorganic materials with laminated crystal structures.
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| 8. |
- Xin, Binbin, et al.
(författare)
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Engineering thermoelectric and mechanical properties by nanoporosity in calcium cobaltate films from reactions of Ca(OH)(2)/Co3O4 multilayers
- 2022
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 4:16, s. 3353-3361
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Tidskriftsartikel (refereegranskat)abstract
- Controlling nanoporosity to favorably alter multiple properties in layered crystalline inorganic thin films is a challenge. Here, we demonstrate that the thermoelectric and mechanical properties of Ca3Co4O9 films can be engineered through nanoporosity control by annealing multiple Ca(OH)(2)/Co3O4 reactant bilayers with characteristic bilayer thicknesses (b(t)). Our results show that doubling b(t), e.g., from 12 to 26 nm, more than triples the average pore size from similar to 120 nm to similar to 400 nm and increases the pore fraction from 3% to 17.1%. The higher porosity film exhibits not only a 50% higher electrical conductivity of sigma similar to 90 S cm(-1) and a high Seebeck coefficient of alpha similar to 135 mu V K-1, but also a thermal conductivity as low as kappa similar to 0.87 W m(-1) K-1. The nanoporous Ca3Co4O9 films exhibit greater mechanical compliance and resilience to bending than the bulk. These results indicate that annealing reactant multilayers with controlled thicknesses is an attractive way to engineer nanoporosity and realize mechanically flexible oxide-based thermoelectric materials.
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| 9. |
- Xin, Binbin, 1989-
(författare)
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Flexible inorganic and hybrid thermoelectric thin films based on layered calcium cobaltate
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the development of wearable and miniaturized electronics, self-sustaining energy sources have drawn extensive attention. Flexible thermoelectric materials and devices is an approach to convert waste heat into electricity as continuous power supply for such applications.Traditional inorganic thermoelectric materials, such as Bi2Te3, PbTe, and SnTe, exhibit high thermoelectric properties, but their disadvantages of toxicity and oxidation when exposed to high temperature in air, as well as the extreme rarity of tellurium, restrict them from widespread use in applications. Compared to conventional thermoelectric materials, oxides, especially misfit-layered Ca3Co4O9, have advantages as thermoelectric materials, not only has the typical advantages of oxides including low cost and good chemical stability at high temperatures, but they are also based on abundant raw materials and have relatively high thermoelectric properties due to the complex structure which composed of CoO2 conductive layers and rock-salt type Ca2CoO3 insulating layers. Many strategies have been used to enhance the thermoelectric performance of Ca3Co4O9. However, inorganic materials are generally rigid, limiting their use in flexible devices. Fully inorganic flexible thermoelectrics can be obtained through novel fabrication technologies, miniaturization, and structural design. Otherwise, organic/inorganic hybrids materials simultaneously combine the respective features of the good flexibility and low thermal conductivity from conducting polymers, and the electrical transport properties from inorganic materials.In order to explore flexible thermoelectric thin films based on layered calcium cobaltate, I have investigated the Ca3Co4O9 and CaxCoO2 systems. Nanoporous Ca3Co4O9 thin films were synthesized using sequential reactive magnetron sputtering and post annealing. The key factors, Ca(OH)2 content, bilayer thickness, and Ca elemental ratio in multilayers film, for the formation of nanoporous Ca3Co4O9 have been studied and can further tailor the porosity and morphology. Nanoporous Ca3Co4O9 with different porosity and discontinuous films with islands of highly textured Ca3Co4O9, effectively constituting distributed nanoparticles, have been obtained. Based on the nanoporous Ca3Co4O9 thin film, flexible double-layer nanoporous Ca3Co4O9/PEDOT:PSS thin films were synthesized by spin-coating PEDOT:PSS into the nanopores.
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| 10. |
- Xin, Binbin, et al.
(författare)
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Growth and optical properties of CaxCoO2 thin films
- 2021
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Ingår i: Materials & design. - : Elsevier Science Ltd. - 0264-1275 .- 1873-4197. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- The layered cobaltates A(x)CoO(2) (A = Li, Na, Ca, Ba, Sr) are of interest for energy applications such as thermoelectrics and batteries. However, it is challenging to obtain these phases in pure from as thin films. Here, phase-pure CaxCoO2 (x similar to 0.5) thin films were obtained by annealing of Ca(OH)(2)/Co3O4 multilayers made by moisture treatment of sputter-deposited CaO/Co3O4 multilayer films. The pure CaxCoO2 thin films exhibit an average optical transmittance of approximately 36% in the visible region and greater than 70% in the near-infrared (NIR) region. In addition, the electrical conductivity can be increased by incorporating a secondary Ca3Co4O9 phase into the CaxCoO2 thin film without large changes in optical properties and Seebeck coefficient. (C) 2021 The Authors. Published by Elsevier Ltd.
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