| 1. |
- Ekström, Erik, 1989-
(author)
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Growth and thermoelectric properties of CaMnO3-based thin films
- 2018
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Licentiate thesis (other academic/artistic)abstract
- The field of them1oelectrics started in early 19th century. Since the discovery of the Seebeck effect and the Peltier effect, thermoelectric modules have found their way into, mostly, niche applications such as radioisotope thermoelectric generators on space missions. Thermoelectric modules can also be used for cooling, utilizing the Peltier effect.Thermoelectrics are promising materials due to the operation nature of the modules. That is, they have no moving parts, no exhaust, long lifetime without maintenance, features that make them attractive for many applications. Despite these promising properties, thermoelectric modules are mostly used in niche applications. The main reason for this is conventional modules with the highest efficiency are commonly made of expensive and/or rare elements which prevents mass production.To tackle this problem, new materials are investigated to find a module that can be made widely available. Oxides are one possibility, where an added benefit is that they are chemically stable even at elevated temperature. The perovskite CaMnO3 is one of the more promising oxides, with elements that are abundant on earth and cheap. The material does suffer from low electrical conductivity which results in a low electrical conductivity and efficiency. A substantial effort has been put in to increase the efficiency of CaMnO3, hut it still needs improvement.In my thesis, I have investigated the CaMnO3 system. CaMnO3 was synthesized using co-reactive RF-magnetron sputtering and post annealing. The synthesis method is already known hut has not been used for deposition of perovskites. I have also demonstrated that this synthesis method can be used to dope CaMnO3 with niobium at appropriate levels for enhancing the efficiency.
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| 2. |
- Albrektson, Anna, 1966-, et al.
(author)
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Cool Nature : Utopian Landscapes in Sweden 1780–1840
- 2022
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In: Sjuttonhundratal. - : UiT The Arctic University of Norway. - 1652-4772 .- 2001-9866. ; 19, s. 94-116
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Journal article (peer-reviewed)abstract
- In this essay, an interdisciplinary group of researchers sets out to address the period 1780–1840 in Sweden in a new way, by placing nature at its centre. With the help of ecocritical and transcultural theory, combined with renewed attention to the Swedish fine arts, learned discourses, and practices, we suggest a new approach to these revolutionary decades. The perceived dissonance, the interplay between climatic conditions and cultural template in early modern and modern Sweden, has not been fully addressed in current research, despite the fact that the relationship between humankind and the environment is a central issue in contemporary society and scholarship. Representations of nature situate the nation, they negotiate the relationship between a sensed reality and an ideal, between human and more-than-human beings. We suggest a focus on the unpredictable space created by negotiations of nature in Swedish representations during this crucial period, and, furthermore, on the ways in which this creative space is charged with utopian possibilities in the early Anthropocene. This is the background and the driving force of the planned research project ‘Cool Nature: Utopian Landscapes in Sweden 1780–1840’.
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| 3. |
- Ekström, Erik, 1989-, et al.
(author)
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Epitaxial Growth of CaMnO3-y Films on LaAlO3 (112 over bar 0) by Pulsed Direct Current Reactive Magnetron Sputtering
- 2022
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In: Physica Status Solidi. Rapid Research Letters. - : Wiley-V C H Verlag GMBH. - 1862-6254 .- 1862-6270. ; 16:4
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Journal article (peer-reviewed)abstract
- CaMnO3 is a perovskite with attractive magnetic and thermoelectric properties. CaMnO3 films are usually grown by pulsed laser deposition or radio frequency magnetron sputtering from ceramic targets. Herein, epitaxial growth of CaMnO3-y (002) films on a (112 over bar 0)-oriented LaAlO3 substrate using pulsed direct current reactive magnetron sputtering is demonstrated, which is more suitable for industrial scale depositions. The CaMnO3-y shows growth with a small in-plane tilt of <approximate to 0.2 degrees toward the (200) plane of CaMnO3-y and the (1 over bar 104) with respect to the LaAlO3 (112 over bar 0) substrate. X-ray photoelectron spectroscopy of the electronic core levels shows an oxygen deficiency described by CaMnO2.58 that yields a lower Seebeck coefficient and a higher electrical resistivity when compared to stoichiometric CaMnO3. The LaAlO3 (112 over bar 0) substrate promotes tensile-strained growth of single crystals. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal antiphase boundaries composed of Ca on Mn sites along and , forming stacking faults.
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| 4. |
- Ekström, Erik, 1989-
(author)
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Epitaxial growth, structure, and thermoelectric properties of CaMn- and V-based oxides
- 2021
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Doctoral thesis (other academic/artistic)abstract
- This thesis is focused on physical vapor deposition, epitaxy, and structural characterization of CaMnO3 and VO2. Environmentally friendly and abundant materials are important for energy savings in applications, e.g., thermoelectrics for waste-heat recycling and thermochromic materials for passive indoor-temperature regulation. CaMnO3 is thermoelectric and VO2 is thermochromic at attractive temperatures for waste heat recycling and passive indoor-temperature regulation, respectively. The two material systems in this thesis were grown by reactive magnetron sputtering. A two-step synthesis process was investigated where rock-salt (Ca,Mn)O was grown by sputtering followed by an annealing step to form the perovskite CaMnO3. CaMnO3 was alloyed with Nb with the purpose to enhance the thermoelectric properties by increasing the number of free carriers, resulting in CaMn1-xNbxO3 (x = 0 – 0.10) films. CaMnO3 was grown on Al2O3 and LaAlO3 while VO2 was grown on muscovite (mica), phase-pure films of the metastable B phase and the stable M1 phase could be grown by controlling the gas flow and pressure. The mica substrate is a material with weakly interacting van der Waals layers in the structure that enable van der Waals epitaxy for the stable VO2 film in M1 phase. The thickness effect on electrical properties in the thermochromic region was investigated as well as proving van der Waals epitaxy. This thesis therefore provides an overall contribution to the understanding of film structure and the control thereof and how it affects the properties of the film.
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| 5. |
- Landälv, Ludvig, 1982-, et al.
(author)
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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
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In: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 34:22, s. 3735-3746
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Journal article (peer-reviewed)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.
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