| 1. |
- Biendicho, Jordi Jacas, et al.
(författare)
-
In situ investigation of commercial Ni(OH)(2) and LaNi5-based electrodes by neutron powder diffraction
- 2015
-
Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 30:3, s. 407-416
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical reactions at both positive and negative electrodes in a nickel metal hydride (Ni-MH) battery during charge have been investigated by in situ neutron powder diffraction. Commercially available beta-Ni(OH)(2) and LaNi5-based powders were used in this experiment as positive and negative electrodes, respectively. Exchange of hydrogen by deuterium for the beta-Ni(OH)(2) electrode was achieved by ex situ cycling of the cell prior to in situ measurements. Neutron diffraction data collected in situ show that the largest amount of deuterium contained at the positive electrode is de-intercalated from the electrode with no phase transformation involved up to similar to 100 mA h/g and, in addition, the 110 peak width for the positive electrode increases on charge. The negative electrode of composition MmNi(3.6)Al(0.4)Mn(0.3)Co(0.7), where Mm = Mischmetal, exhibits a phase transformation to an intermediate hydride gamma phase first and then to the beta phase on charge. Unit cell dimensions and phase fractions have been investigated by Rietveld refinement of the crystal structure.
|
|
| 2. |
- Ciammaruchi, Laura, et al.
(författare)
-
Stability of organic solar cells with PCDTBT donor polymer : An interlaboratory study
- 2018
-
Ingår i: Journal of Materials Research. - New York : Cambridge University Press. - 0884-2914 .- 2044-5326. ; 33:13, s. 1909-1924
-
Tidskriftsartikel (refereegranskat)abstract
- This work is part of the interlaboratory collaboration to study the stability of organic solar cells containing PCDTBT polymer as a donor material. The varieties of the OPV devices with different device architectures, electrode materials, encapsulation, and device dimensions were prepared by seven research laboratories. Sets of identical devices were aged according to four different protocols: shelf lifetime, laboratory weathering under simulated illumination at ambient temperature, laboratory weathering under simulated illumination, and elevated temperature (65 degrees C) and daylight outdoor weathering under sunlight. The results generated in this study allow us to outline several general conclusions related to PCDTBT-based bulk heterojunction (BHJ) solar cells. The results herein reported can be considered as practical guidance for the realization of stabilization approaches in BHJ solar cells containing PCDTBT.
|
|
| 3. |
- Hallberg, Robert T., et al.
(författare)
-
Palladium seeded GaAs nanowires
- 2016
-
Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 31:2, s. 175-185
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a detailed investigation of the growth of palladium-seeded GaAs nanowires. Nanowires grown on GaAs (111)B substrates consist of three different morphologies, denoted as curly (containing multiple kinks), inclined (relative to the substrate, such as 〈001〉), and vertical. We show that the relative yield of the different types is controllable by a combination of V/III ratio and temperature, where vertical and inclined nanowires are promoted by a high temperature and low V/III ratio. These growth conditions are expected to promote a higher Ga incorporation into the Pd particle, which is confirmed by energy dispersive x-ray analysis. We propose that the observed relationship between particle composition and nanowire morphology may be related to the particle phase, with liquid particles promoting straight nanowire growth. In addition, particles at the tips of nanowires are sometimes observed to be smaller than the initial particle size, suggesting that Pd has been lost during the growth process. Finally, we demonstrate the importance of initial particle size-control to interpret diameter changes after growth.
|
|
| 4. |
|
|
| 5. |
- Hedayati, Raheleh, et al.
(författare)
-
Material aspects of wide temperature range amplifier design in SiC bipolar technologies
- 2016
-
Ingår i: Journal of Materials Research. - : Cambridge University Press. - 0884-2914 .- 2044-5326. ; 31:19, s. 2928-2935
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide (SiC) is the main semiconductor alternative for low loss high voltage devices. The wide energy band gap also makes it suitable for extreme environment electronics, including very high temperatures. Operating integrated electronics at 500-600 °C poses several materials challenges. However, once electronics is available for these high temperatures, the added challenge is designing integrated circuits capable of operating in the entire range from room temperature to 500 °C. Circuit designers have to take into account parameter variations of resistors and transistors, and models are needed for several temperatures. A common circuit design technique to manage parameter variations between different transistors, without wide temperature variations, is to use negative feedback in amplifier circuits. In this paper we show that this design technique is also useful for adapting to temperature changes during operation. Two different amplifier designs in SiC are measured and simulated from room temperature up to 500 °C.
|
|
| 6. |
- Huang, Shuo, et al.
(författare)
-
Elasticity of high-entropy alloys from ab initio theory
- 2018
-
Ingår i: Journal of Materials Research. - : Cambridge University Press. - 0884-2914 .- 2044-5326. ; 33:19, s. 2938-2953
-
Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys (HEAs) consisting of multiprincipal elements have demonstrated many interesting structural, physical, and chemical properties for a wide range of applications. This article is a review of the current theoretical research on the elastic parameters of HEAs. The performance of various ab initio-based computational models (effective medium and supercell approaches) is carefully analyzed. Representative theoretical elastic parameters of different HEAs, including single-crystal elastic constants, polycrystalline elastic moduli, elastic anisotropy, and Debye temperature, are presented and discussed. For comparison, simple mixtures of the elastic moduli of pure elements are calculated and contrasted with the ab initio results. The present work provides a reference for future theoretical investigation of the micromechanical properties of systems based on HEAs. Copyright
|
|
| 7. |
- Landälv, Ludvig, 1982-, et al.
(författare)
-
Phase evolution of radio frequency magnetron sputtered Cr-rich (Cr,Zr)(2)O-3 coatings studied by in situ synchrotron X-ray diffraction during annealing in air or vacuum
- 2019
-
Ingår i: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 34:22, s. 3735-3746
-
Tidskriftsartikel (refereegranskat)abstract
- The phase evolution of reactive radio frequency (RF) magnetron sputtered Cr0.28Zr0.10O0.61 coatings has been studied by in situ synchrotron X-ray diffraction during annealing under air atmosphere and vacuum. The annealing in vacuum shows t-ZrO2 formation starting at similar to 750-800 degrees C, followed by decomposition of the alpha-Cr2O3 structure in conjunction with bcc-Cr formation, starting at similar to 950 degrees C. The resulting coating after annealing to 1140 degrees C is a mixture of t-ZrO2, m-ZrO2, and bcc-Cr. The air-annealed sample shows t-ZrO2 formation starting at similar to 750 degrees C. The resulting coating after annealing to 975 degrees C is a mixture of t-ZrO2 and alpha-Cr2O3 (with dissolved Zr). The microstructure coarsened slightly during annealing, but the mechanical properties are maintained, with no detectable bcc-Cr formation. A larger t-ZrO2 fraction compared with alpha-Cr2O3 is observed in the vacuum-annealed coating compared with the air-annealed coating at 975 degrees C. The results indicate that the studied pseudo-binary oxide is more stable in air atmosphere than in vacuum.
|
|
| 8. |
- Olsson, Simon, et al.
(författare)
-
Mechanical and Tribological Properties of AlCuFe Quasicrystal and Al(Si)CuFe Approximant Thin Films
- 2016
-
Ingår i: Journal of Materials Research. - : Cambridge University Press. - 0884-2914 .- 2044-5326. ; 31:2, s. 232-240
-
Tidskriftsartikel (refereegranskat)abstract
- Multilayered thin films of Al/Cu/Fe have been prepared by magnetron sputtering and annealed into the quasicrystalline or approximant phases, for Al2O3 or Si substrates, respectively. The nanomechanical and nanotribological properties; hardness, elastic modulus, friction and toughness, have been measured using a triboindenter and analytical methods. The approximant phase, annealed at 600 °C for 4 h, proved to be harder and had higher elastic modulus values than the quasicrystalline phase, about, 15.6 GPa and 258 GPa, respectively. The fracture toughness of the approximant, <0.1 MPa/m½, was however inferior to that of the quasicrystals with 1.5 MPa/m½. The friction coefficients were measured in a range of 0.10-0.14 for the quasicrystalline and approximant thin films.
|
|
| 9. |
- Reddy, S. R., et al.
(författare)
-
Development and homogeneity of microstructure and texture in a lamellar AlCoCrFeNi2.1 eutectic high-entropy alloy severely strained in the warm-deformation regime
- 2019
-
Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 34:5, s. 687-699
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of severe warm rolling on microstructure and texture homogeneities was investigated in a lamellar (L12 + B2) AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA). The EHEA 90% warm-rolled at 400 °C showed disordering of the L12 phase and a remarkable increase in hardness. A much finer microstructure was observed on ND-RD (Normal Direction-Rolling Direction) plane as compared with that on the RD-TD (Rolling Direction-Transverse Direction) plane. The L12/Face Centered Cubic (FCC) phase developed α-fiber texture ND//(110) with a particularly strong brass ({110}(112)) component, while the B2 phase developed the usual RD (//(110) and ND (//(111)) fibers. Nevertheless, inhomogeneities in texture were noticed. Upon annealing at 800 °C, the ND-RD showed an ultrafine microduplex structure, while the RD-TD showed a retained lamellar structure. A rather uniform microduplex structure evolved after annealing at 1200 °C due to the accelerated kinetics of transformation at higher temperatures. The L12/FCC phase showed the retention of the α-fiber components, while the B2 phase showed stronger ND-fiber after annealing, although inhomogeneities in texture existed.
|
|
| 10. |
- Schleife, A., et al.
(författare)
-
Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂
- 2017
-
Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 32:1, s. 56-63
-
Tidskriftsartikel (refereegranskat)abstract
- Materials for scintillator radiation detectors need to fulfill a diverse set of requirements such as radiation hardness and highly specific response to incoming radiation, rendering them a target of current materials design efforts. Even though they are amenable to cutting-edge theoretical spectroscopy techniques, surprisingly many fundamental properties of scintillator materials are still unknown or not well explored. In this work, we use first-principles approaches to thoroughly study the optical properties of four scintillator materials: NaI, LaBr3, BaI2, and SrI2. By solving the Bethe-Salpeter equation for the optical polarization function we study the influence of excitonic effects on dielectric and electron-energy loss functions. This work sheds light into fundamental optical properties of these four scintillator materials and lays the ground-work for future work that is geared toward accurate modeling and computational materials design of advanced radiation detectors with unprecedented energy resolution. Copyright © Materials Research Society 2016.
|
|
| 11. |
- Stuer, Michael, et al.
(författare)
-
Comparison of apparent activation energies for densification of alumina powders by pulsed electric current sintering (spark plasma sintering) and conventional sintering-toward applications for transparent polycrystalline alumina
- 2017
-
Ingår i: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 32:17, s. 3309-3318
-
Tidskriftsartikel (refereegranskat)abstract
- In the quest for high real in-line transmittances for transparent polycrystalline alumina (PCA), we need defect free processing. One of the biggest advances in producing high density defect free ceramics over recent years has been the advent of spark plasma sintering (SPS) or pulsed electric current sintering. The production of PCA with high transmittances >60% has been demonstrated, but the mechanisms behind this fast, pressure aided sintering method are still much debated. Here, we investigate the sintering of doped a-alumina powders using traditional and pulsed electric current dilatometry. We demonstrate that at the final sintering stage, there is no major difference in the sintering mechanisms between conventional sintering and SPS sintering. High densification rates occurring in SPS are shown to be related to powder reorientation at the very early sintering stage and viscous-flow dominated densification in the intermediate sintering cycle. This paper clarifies what parameters in the processing-sintering domain have to be improved for even higher real in-line transmittances for PCA.
|
|
| 12. |
- Yang, Zhi-biao, et al.
(författare)
-
Assessing elastic property and solid-solution strengthening of binary Ni-Co, Ni-Cr, and ternary Ni-Co-Cr alloys from first-principles theory
- 2018
-
Ingår i: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 33:18, s. 2763-2774
-
Tidskriftsartikel (refereegranskat)abstract
- The elastic properties and solid-solution strengthening (SSS) of the binary Ni-Co and Ni-Cr, and ternary Ni-Co-Cr alloys were investigated by the first-principles method. The results show that both Co and Cr increase lattice parameters of the binary alloys linearly. However, nonlinearity is found in compositional dependence of lattice parameters in the ternary Ni-Co-Cr alloys, that is, Co increases but decreases the lattice parameter at low and high Cr concentrations, respectively. Co increases the bulk, shear, and Young's moduli (B, G, and E), while Cr increases B but decreases G and E in the binary alloys. In the ternary Ni-Co-Cr alloys, G and E have a similar compositional dependence to those in the binary alloys, except for B. Based on the Labusch model, the SSS parameter of Ni-Cr is larger than that of Ni-Co. The SSS effect increases significantly with Cr addition, especially at low Co concentrations in the ternary Ni-Co-Cr alloys. Meanwhile, it increases mildly with Co addition at low Cr concentrations but decreases with Co addition at high Cr concentrations.
|
|
