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Rahman, Jamil Ur; Gunnæs, Anette Eleonora; Finstad, Terje Gunnar; Løvvik, Ole Martin & Almeida Carvalho, Patricia
(2023).
Structure of a high entropy Heusler antimonide.
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Bazioti, Kalliopi; Gorantla, Sandeep; Ravuri, SyamSai; Wrobel, Pawel S.; Sunding, Martin Fleissner & Sartori, Sabrina
[Vis alle 9 forfattere av denne artikkelen]
(2023).
In situ and operando transmission electron microscopy: real-time nanoscale insights into emerging materials for batteries.
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Bazioti, Kalliopi; Gorantla, Sandeep; Ravuri, SyamSai; Wrobel, Pawel S.; Sunding, Martin Fleissner & Sartori, Sabrina
[Vis alle 9 forfattere av denne artikkelen]
(2023).
In situ and operando transmission electron microscopy investigations of MXene-based anodes for Li-ion all-solid-state batteries.
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Bazioti, Kalliopi; Gorantla, Sandeep; Sunding, Martin Fleissner; Sartori, Sabrina; Diplas, Spyridon & Bachmatiuk, Alicja
[Vis alle 7 forfattere av denne artikkelen]
(2023).
In situ and Operando Transmission Electron Microscopy investigations of novel 2D-based anodes for Li-ion all-solid-state batteries
.
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Rahman, Jamil Ur; Sunding, Martin Fleissner; Løvvik, Ole Martin; Gunnæs, Anette Eleonora; Finstad, Terje Gunnar & Almeida Carvalho, Patricia
(2023).
Deciphering the structure of a high-entropy Heusler antimonide.
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Løvvik, Ole Martin; Rahman, Jamil Ur; Finstad, Terje Gunnar; Gunnæs, Anette Eleonora & Almeida Carvalho, Patricia
(2022).
Thermoelectric properties of multiple component (high entropy) silicides and antimonides.
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Løvvik, Ole Martin; Carvalho, Patricia A.; Stange, Marit Synnøve Sæverud; Sunding, Martin Fleissner; Rajput, Kalpna & Larsen, Aleksander Amble
[Vis alle 9 forfattere av denne artikkelen]
(2022).
Elastocaloric cooling with TiNiCuZr alloys?
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Reiersen, Magnus; Gunnæs, Anette Eleonora; S. Azar, Amin; Diplas, Spyridon; Du, Qiang & M`hamdi, Mohammed
(2022).
Accelerated material development for laser powder-bed fusion using the arc melting process.
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Poulia, Anthoula; Larsen, Aleksander; Joachim Seland, Graff; Diplas, Spyros; Gunnæs, Anette Eleonora & Mikheenko, Pavlo
(2022).
Imaging Magnetic Domain Structure of a High Entropy Alloy: Effect of Applied Magnetic Field.
Vis sammendrag
High-Entropy Alloys (HEAs) are recently introduced materials consisting of numerous—at least five—elements in nearly equal-atomic concentrations. Studying them, previously unexplored phase fields in multidimensional phase diagrams are now being explored. The HEA concept is based on a thermodynamic balance between mixing entropy and enthalpy, which defines values of several critical parameters that determine the formation of simple or complicated phases. Physical properties, like magnetism, are of great interest for these materials, even though they have not been extensively analyzed so far. Particularly, the exploration of the magnetic domain structure and its correlation with the micro- and nano-structural features of the materials is of high scientific value. In this work, we study the influence of the magnetic history on the alteration of the magnetic domain patterns in polycrystalline FeCoNiAl0.9Mn0.9 High Entropy Alloy (HEA). For the study, we introduce a combinatorial method of Electron Backscatter Diffraction and Magnetic Force Microscopy imaging, which reveals specific magnetic domain structures in the grains of different crystallographic orientations. It is found that in the HEA polycrystal, an increase of the applied magnetic field affects the formation of magnetic domains and leads to a transition from a labyrinth-like pattern to a dotted domain configuration, which is expressed differently in the differently oriented grains.
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Bazioti, Kalliopi; Gorantla, Sandeep; Sunding, Martin Fleissner; Sartori, Sabrina; Diplas, Spyridon & Bachmatiuk, Alicja
[Vis alle 7 forfattere av denne artikkelen]
(2022).
In situ and Operando Transmission Electron Microscopy investigations of MXenes for Li-ion all-solid-state batteries.
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Bazioti, Kalliopi; Gorantla, Sandeep; Sunding, Martin Fleissner; Sartori, Sabrina; Diplas, Spyridon & Bachmatiuk, Alicja
[Vis alle 7 forfattere av denne artikkelen]
(2022).
Novel 2D-based anodes for Li-ion all-solid-state batteries.
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Pop-Ghe, Patricia; Amundsen, Monika; Zamponi, Christiane; Gunnæs, Anette Eleonora & Quandt, Eckhard
(2021).
Direct observation of intermediate twinning in the phase
transformations of ferroelectric potassium sodium niobate.
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Poulia, Anthoula; S. Azar, Amin; Bazioti, Kalliopi; Gunnæs, Anette Eleonora; Mikheenko, Pavlo & Diplas, Spyridon
(2021).
Investigation of High Entropy Alloys via Magnetic Force Microscopy.
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Poulia, Anthoula; S. Azar, Amin; Bazioti, Kalliopi; Gunnæs, Anette Eleonora; Mikheenko, Pavlo & Diplas, Spyridon
(2021).
Additively manufactured FeCoNi(AlMn)x high entropy alloys: Mechanical and magnetic properties investigation.
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Poulia, Anthoula; S. Azar, Amin; Gunnæs, Anette Eleonora; Bazioti, Kalliopi; Mikheenko, Pavlo & Diplas, Spyridon
(2021).
Tailoring mechanical and magnetic properties of the FeCoNi(AlMn)x high entropy alloys via compositional alterations.
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Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; S. Azar, Amin; Mikheenko, Pavlo & Diplas, Spyridon
[Vis alle 7 forfattere av denne artikkelen]
(2021).
Structural evolution of FeCoNi(AlMn)x high-entropy alloy and impact on magnetic properties: nano-scale STEM-EELS investigations.
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Almeida Carvalho, Patricia; Rahman, Jamil Ur; Soltani, Nayereh; Schrade, Matthias; Stange, Marit Synnøve Sæverud & Gunnæs, Anette Eleonora
[Vis alle 8 forfattere av denne artikkelen]
(2021).
Functional high entropy antimonides and silicides.
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Almeida Carvalho, Patricia; Mayandi, Jeyanthinath; Rahman, Jamil Ur; Soltani, Nayereh; Schrade, Matthias & Gunnæs, Anette Eleonora
[Vis alle 9 forfattere av denne artikkelen]
(2021).
Exploring the structure of high entropy oxides, silicides and antimonides for functional applications.
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Larsen, Aleksander; Poulia, Anthoula; S. Azar, Amin; Bazioti, Kalliopi; Almeida Carvalho, Patricia & Gunnæs, Anette Eleonora
[Vis alle 9 forfattere av denne artikkelen]
(2021).
Identifying Magnetic Phases in Additively Manufactured High-Entropy Alloy FeCoNiAlxMnx.
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Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; S. Azar, Amin; Mikheenko, Pavlo & Diplas, Spyridon
[Vis alle 7 forfattere av denne artikkelen]
(2021).
Advanced Scanning Transmission Electron Microscopy investigations of FeCoNi(AlMn)x high-entropy alloy: nanoscale structure and impact on magnetic properties.
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Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Almeida Carvalho, Patricia; S. Azar, Amin & Mikheenko, Pavlo
[Vis alle 8 forfattere av denne artikkelen]
(2021).
STEM-EELS investigations and Lorentz microscopy unravelling the
structural evolution of FeCoNi(AlMn)x high-entropy alloy
and its impact on magnetic properties.
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Poulia, Anthoula; S. Azar, Amin; Svec, Peter; Bazioti, Kalliopi; Belle, Branson & Gunnæs, Anette Eleonora
[Vis alle 8 forfattere av denne artikkelen]
(2020).
Nanoscale Magnetic Properties of Additively Manufactured FeCoNiAlxMnx High-Entropy Alloys.
Vis sammendrag
Magnetic properties of High-Entropy Alloys based on the Fe-Co-Ni-Al-Mn system are reported. High-Entropy Alloys are cutting-edge technological materials containing five or more elements in relatively high concentrations (5–35 at.%) within one or several solid-state solutions. These solutions are stabilized at the nanometer scale due to the high contribution of the mixing entropy to the Gibbs free energy, which can overcome the enthalpic contribution. Two magnetic alloys are found in FeCoNiAlxMnx (1.6 at.% x 7.8 at.%) samples processed by laser metal deposition. The magnetic techniques used to screen the materials were magneto-optical imaging and magnetic force microscopy. The former allows characterizing magnetic properties within the mm-μm scale, while the latter is efficient down to the nanometer scale. Magnetic screening confirms the importance of the nanostructure in defining magnetic properties of the alloys, and the trends in the magnetic behavior as a function of the alloy composition are revealed. The experimental results suggest that it is possible to form unique alloys, which may outperform conventional magnetic materials used in a variety of applications such as transformers, screening shields and wind power generators.
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Løberg, Monika; Karlsen, Ole Bjørn; Løvvik, Ole Martin; Almeida Carvalho, Patricia & Gunnæs, Anette Eleonora
(2019).
Characterization of phase transformations within the Cu-Pd-Sn system - a possible shape memory alloy for energy conversion.
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Løberg, Monika; Pike, Nicholas; Almeida Carvalho, Patricia; Karlsen, Ole Bjørn; Løvvik, Ole Martin & Gunnæs, Anette Eleonora
(2019).
Martensitic-like phase transformations within the Cu-Pd-Sn system
.
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Løberg, Monika; Løvvik, Ole Martin; Almeida Carvalho, Patricia; Karlsen, Ole Bjørn & Gunnæs, Anette Eleonora
(2019).
Phase Transformations within the Cu-Pd-Sn system.
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Løberg, Monika; Pike, Nicholas; Karlsen, Ole Bjørn; Almeida Carvalho, Patricia; Løvvik, Ole Martin & Gunnæs, Anette Eleonora
(2019).
Characterization of phase transforming, Heusler based (Cu-Pd-Sn), alloys for energy harvesting. .
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Sunding, Martin Fleissner; Løberg, Monika; S. Azar, Amin; Stange, Marit Synnøve Sæverud; Almeida Carvalho, Patricia & Karlsen, Ole Bjørn
[Vis alle 10 forfattere av denne artikkelen]
(2019).
The Need for a Multi-Technique Approach in the Search for New Phase-Transforming Materials.
Vis sammendrag
Introduction/Purpose
Reversible diffusionless first-order phase transformations are a fundamental part of phase change materials and shape memory alloys
[1]. Some of
these materials even possess useful physical characteristics that show abrupt changes e.g. in their electrical[2] and magnetic
[3] polarizations. These phase transformations can be studied using multiple techniques, enabling access to different types of information including length scales and time periods, but how should this characterisation be approached? Methods TEM studies give highly relevant data in this field of research, from detailed crystallographic structures, to relative orientations between grains and
phases and to the phase transformation temperature. However, TEM analyses are time consuming and requires small sample sizes and ad hoc preparation. High-throughput measurement techniques are thus required in the search for improved compositions and new materials in order to
rapidly assess the properties of many samples or samples with graded composition
[4]. Optical methods (for example unpolarised and polarised microscopy and thermal imaging) and electric conductivity measurements can for example be used to map phase transformation temperatures much faster and on much larger areas than traditional TEM techniques. XRD and SEM-EDS-EBSD can then be applied to obtain initial
crystallographic and microstructure information on an intermediate size scale, before TEM is applied for the in-depth study of the most relevant
compositions. Results We applied this multi-pronged approach in the search for Heusler and half-Heusler alloys with a low temperature martensitic phase transformation
and with low thermal hysteresis, with potential applications in waste heat energy harvesting.
Conclusions Drawing advantage of the strengths of multiple analysis techniques – with respect to the obtainable information, the sample size and/or the time
frame of the analyses – renders the search for new phase change materials more effective. It enables faster identification of potential target
compositions and of sample areas optimal for in depth studies.
Selected references
[1] David Dye, Nature Materials14 (8), 760 (2015).
[2] M. M. Vopson, Critical Reviews in Solid State and Materials Sciences40 (4), 223 (2015).
[3] L. Huang, D. Y. Cong, L. Ma, Z. H. Nie, Z. L. Wang, H. L. Suo, Y. Ren, and Y. D. Wang, Applied Physics Letters108 (3) (2016).
[4] M. L. Green, C. L. Choi, J. R. Hattrick-Simpers, A. M. Joshi, I. Takeuchi, S. C. Barron, E. Campo, T. Chiang, S. Empedocles, J. M. Gregoire, A. G. Kusne, J. Martin, A. Mehta, K. Persson, Z. Trautt, J. Van Duren, and A.
Zakutayev, Applied Physics Reviews 4 (1), 011105 (2017).
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Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Wachowski, Sebastian Lech; Mielewczyk-Gryn, Aleksandra & Balaguer, Maria
[Vis alle 9 forfattere av denne artikkelen]
(2019).
Hydration and hydrogenation of mixed conducting BaGd1‑xLaxCo2O6‑δ (BGLC).
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Kalyva, Maria Evangelou; Redekop, Evgeniy; Johansson, Niclas; Urpelainen, Samuli; Gunnæs, Anette Eleonora & Diplas, Spyridon
[Vis alle 7 forfattere av denne artikkelen]
(2019).
AP-XPS study of bimetallic PtCu nanoparticles supported on SiO2 films.
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de Ruiter, Lisa; Austrheim, Håkon Olaf; Dysthe, Dag Kristian & Gunnæs, Anette Eleonora
(2018).
Quartz weathering associated with magnesium silicate hydrate cement precipitation.
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de Ruiter, Lisa; Austrheim, Håkon Olaf; Gunnæs, Anette Eleonora & Dysthe, Dag Kristian
(2018).
Quartz dissolution and M-S-H cement precipitation in a high pH ultramafic system.
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Løberg, Monika; Løvvik, Ole Martin & Gunnæs, Anette Eleonora
(2018).
Energy Conversion using Phase Transforming Materials - the Cu-Pd-Sn system.
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Løberg, Monika; Løvvik, Ole Martin & Gunnæs, Anette Eleonora
(2018).
Martensitic like phase transformations in the Cu-Pd-Sn system.
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Strandbakke, Ragnar; Gunnæs, Anette Eleonora; Carvalho, Patricia A.; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian & Balaguer, Maria
[Vis alle 8 forfattere av denne artikkelen]
(2018).
Coupled hydration, cation reorganization and red-ox in MIEC perovskites .
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Gunnæs, Anette Eleonora
(2017).
Evaluation of a thermoelectric p-n junction at
the macro and nano scale by X-ray and electron probe techniques.
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Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Gunnæs, Anette Eleonora & Ulyashin, Alexander
(2017).
On the evolution of properties of ITO layers deposited on crystalline and amorphous Si upon heat treatments.
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Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Ramasse, Quentin; Gunnæs, Anette Eleonora & Ulyashin, Alexander
(2017).
A high resolution electron microscopy and spectroscopy study of interfaces in Si-based solar cell heterojunctions.
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Gunnæs, Anette Eleonora; Diplas, Spyros & Ulyashin, Alexander G.
(2017).
A TEM and XPS study of epitaxially grown amorphous hydrogenated silicon in solar cell structures.
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Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Berland, Kristian; Gunnæs, Anette Eleonora & Persson, Clas
[Vis alle 8 forfattere av denne artikkelen]
(2017).
Structural Investigation of Ti1-xHfxNiySn Half-Heusler Compounds.
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Berland, Kristian; Eliassen, Simen Nut Hansen; Schrade, Matthias; Tofan, Raluca; Guzik, Matylda Natalia & Gunnæs, Anette Eleonora
[Vis alle 11 forfattere av denne artikkelen]
(2017).
Using theory to understand
thermoelectric materials.
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Gunnæs, Anette Eleonora
(2016).
Nanoscience with TEM at the Center for Material Science and Nanotechnology/NORTEM, Oslo, Norway.
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Granerød, Cecilie Skjold; Nguyen, Phuong Dan; Gunnæs, Anette Eleonora & Prytz, Øystein
(2016).
The Structure Physics group.
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Lervik, Adrian; Bjørheim, Tor Svendsen; Nguyen, Phuong Dan; Diplas, Spyridon; Haugsrud, Reidar & Gunnæs, Anette Eleonora
(2016).
Chemical and Structural Investigations of Grain Boundaries in Y-Doped BaZrO3.
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Schrade, Matthias; Echevarria-Bonet, Cristina; Eliassen, Simen Nut Hansen; Berland, Kristian; Persson, Clas & Tofan, Raluca
[Vis alle 9 forfattere av denne artikkelen]
(2016).
Thermal Properties of XNiSn(X = Hf, Zr, Ti) half Heusler Alloys.
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Schrade, Matthias; Echevarria-Bonet, Cristina; Guzik, Matylda Natalia; Tofan, Raluca; Gunnæs, Anette Eleonora & Eliassen, Simen Nut Hansen
[Vis alle 10 forfattere av denne artikkelen]
(2016).
Thermal properties of XNiSN (X = Ti, Zr, Hf) half Heusler alloys.
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Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian
[Vis alle 10 forfattere av denne artikkelen]
(2016).
The effect of spark plasma sintering on structure and phase stability in half-Heusler thermoelectric alloys.
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Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian
[Vis alle 10 forfattere av denne artikkelen]
(2016).
Microstructural characterization of spark plasma sintered (X,X’)NiSn half‐Heusler alloys.
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Lervik, Adrian; Haugsrud, Reidar; Diplas, Spyridon & Gunnæs, Anette Eleonora
(2015).
A TEM approach to BZY.
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Ulvestad, Asbjørn; Mæhlen, Jan Petter; Andersen, Hanne Flåten; Gunnæs, Anette Eleonora; Prytz, Øystein & Kirkengen, Martin
(2015).
Characterization of PECVD-Grown a-SiC:H for use as Coating for Silicon Thin Film Anodes in Li-Ion Batteries.
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Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora & Carbalho, Partricia
[Vis alle 9 forfattere av denne artikkelen]
(2015).
Nano Improves Thermoelectric Performance.
Vis sammendrag
The rule of thumb for improving the performance of thermoelectric materials is to reduce the thermal conduction, which attributes to electron transport and phonon transport. Phonons are characterized by different wavelength, Short wavelength phonons are scattered by impurity atoms in alloyed matels, Mid- and Long wavelength phonns are scattered by the iuinterfaces. Nanostructuring can engineer the phonon transport by introduce numerous grain boundaries, thus increasing phonon scattering, further improving thermal resistance. The aim of the present study is the nano-grains of the thermoelectric material ZnSb and the correlation with thermal transport measurements. We explored cryomilling (by ball-milling powders at Cryogenic temperature) as a technique to created nano—powders of ZnSb for pressing into pellets. The effect of cryomilling flowed by hot-pressing of undoped ZnSb was investigated.
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Echevarria-Bonet, Cristina; Tofan, Raluca; Schrade, Matthias; Gunnæs, Anette Eleonora; Persson, Clas & Sørby, Magnus Helgerud
[Vis alle 7 forfattere av denne artikkelen]
(2015).
Enhancement of the thermoelectric properties in nanostructured half-Heusler alloys.
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Fjellvåg, Øystein Slagtern; Sjåstad, Anja Olafsen; Haugsrud, Reidar & Gunnæs, Anette Eleonora
(2015).
Investigation of Novel Hydride Oxides for Holistic Understanding of Functional Materials.
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Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora & Luxsacumar, Sivakanesar
[Vis alle 7 forfattere av denne artikkelen]
(2014).
Nanostructuring by Cryomilling of Undoped ZnSb.
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Løvvik, Ole Martin; Song, Xin; Valset, Kjetil; Flage-Larsen, Espen; Fjeld, Harald & Graff, Joachim Seland
[Vis alle 14 forfattere av denne artikkelen]
(2014).
Thermoelectric materials from first principles to final applications: Basic and applied thermoelectrics in Oslo.
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Roaldset, Elen; Bering, Dag; Aerts, Maarten & Gunnæs, Anette E.
(2013).
Kaolinite Group minerals from weathered anorthosite, SW Norway.
Berichte derDeutschen Ton- und Tonmineralgruppe e.V..
ISSN 1432-7007.
15,
s. 27–27.
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Qureishy, Thomas; Hansen, Vidar; Karlsen, Ole Bjørn; Gunnæs, Anette Eleonora & Taftø, Johan
(2012).
Superstructures in Mg2Si1-xSnx.
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Solemsli, Bjørn Gading; Olsbye, Unni; Gunnæs, Anette Eleonora & Gutterød, Emil Sebastian
(2020).
A Study of Catalytic Pt Nanoparticles inside a Nano-porous Functionalized UiO MOF-matrix for CO2-Hydrogenation
.
Universitetet i Oslo.
Vis sammendrag
Hydrogenation of carbon dioxide hasreceivedincreasingattentionin catalytic research the last decade as a sustainable alternativeforproducing high value chemicals thattodayare produced fromfossil fuels. The aim of this thesis has been two-fold: First, to study Pt nanoparticles formed in various UiO-66 and -67 metal-organic frameworks (MOFs) by Transmission Electron Microscopy (TEM), and second, to study the Pt-containing MOFs as catalysts for the CO2hydrogenation reaction.Three Zr-based UiO-66 MOF and nineUiO-67 MOF samples containing different amountsof functionalized linkers were impregnated withdifferent amounts ofK2PtCl4and reduced in H2at 350 ̊C for 4 hours to form Pt nanoparticles embedded in the MOF matrix.The samples were then testedin a H2/CO2feed at 8 bar and 170 ̊Cfor the hydrogenation reaction. After testing,TEMwas used to investigate the formation of Pt nanoparticles andtheir relationship with the surrounding MOF structure.
The study revealed that, despite variable the linkers in the MOF,the conversion of CO2isdominated bythe reverse water-gas shift reaction,suggestingthat the linkers donot partakethe reactions mechanisms. Analysis usingTEMrevealedthat the Pt nanoparticles grow independently of its surroundings inside the MOFs with no observable growth relationshipwith the MOF. The nanoparticles are seen to grow into octahedral crystals that are larger than the pores in the framework. Samples with different amountsof missing linker type defects show that the presence of open Zr-node sitesenhances the selectivity towards methanol. A sample of Pt-functionalized UiO-67 with 10% [2,2’-bipyridine]5,5’-dicaboxylicacidlinker was oxidised toinduce missing linkerdefects post synthetically. After reduction in H2at 350 ̊C for 4 hours, the sample was oxidized in situin synthetic air for three different time spans. Careful analysis with N2-adsroption and TEM revealedthat the structure of the MOF deteriorates and loses accessible surface area with increasing timeon steam, while keeping the dispersion of the Pt nanoparticles. PXRD analysis revealedthe formation of tetragonal ZrO2. Extensive testsfrom 1-30 bar and 170-375 ̊C reveal a lower conversion and higher selectivity towards methanol for a fully calcined sample, indicating that the Zr-nodes behave similarlyto non-MOF ZrO2supports. Transient kinetic studies of the parent UiO-67 sample revealedthat the sample behaves similarlytopreviously studied systemsby Gutterød et al., and showed the presence of an inverse kinetic isotope effect for methane and methanolformation upon H2/D2exchange.
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Løberg, Monika & Gunnæs, Anette Eleonora
(2017).
Influence of Mn Stoichiometry on the Structure and Thermoelectric Properties of CaMn(1+y)O(3-d).
Universitetet i Oslo.
Vis sammendrag
The energy consumption of present day society is ever increasing and the sources for more and
cleaner energy is sought for. A possible contributor are thermoelectric generators, which convert
parts of a heat flux directly into electrical energy. Unfortunately, the efficiency of current
generators is too low for large scale commercialization, and new and better materials must be
designed.
In the present master project, the performance of n-type thermoelectric oxide CaMn(1+y)O(3-d) is
attempted improved by creating precipitates within the nano-range. The precipitates could be
anticipated to enhance phonon scattering, thereby lowering thermal conductivity and enhance
the overall thermoelectric properties of the material. A sample series of CaMn(1+y)O(3-d), with
composition y = 0, 0.020 , 0.036, 0.074 and 0.10, has been synthesized by solid state reaction
and the microstructure and thermoelectric properties were characterized.
Secondary phase, CaMn2O4, precipitates were found from X-ray diffraction and Scanning Electron
Microscopy in the size range 5-10 um. Further investigations into the presence of nanoprecipitates
were performed by Transmission Electron Microscopy finding no areas enriched in
manganese within the CaMnO3 matrix. Electrical resistivity and Seebeck coefficient were measured
from room temperature up to 600C finding a resistivity ranging from 20 - 100 mOhm cm
and Seebeck coefficient from -300 to -200 uVK-1, showing no trend with manganese content.
Thermal conductivity measurements were performed, showing a thermal conductivity between
2.3 - 3.6 Wm-1K-1, however no trend with varying manganese content was observed. Further,
the obtained thermoelectric data was compared with samples fabricated using a different synthesis
method, yielding similar results and no significant variations was observed. The absence of
a Mn-dependency in all transport parameters was carefully confirmed by a thorough investigation
of potential experimental influences, like sample porosity, impurity level and measurement
uncertainty. Finally, the results are qualitatively rationalized using a simple Callaway model
for the thermal conductivity.
The concluding remarks are that all manganese excess will manifest as secondary phase CaMn2O4
and no manganese rich precipitates will exist within the CaMnO3 matrix. The variation in manganese
content does not influence the thermoelectric properties of CaMn(1+y)O(3-d).
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