Monika Løberg

• Løberg, Monika (2019). Energy Recovery using Shape Memory Alloys.
• Løberg, Monika (2019). Huskemetaller - hva er de, hva husker de?.
• Løberg, Monika (2019). Huskemetaller - hva er de, hva husker de, og hvordan kan de gjøre verden til et bedre sted?.
• 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.
• Løberg, Monika; Løvvik, Ole Martin; Almeida Carvalho, Patricia; Karlsen, Ole Bjørn & Gunnæs, Anette Eleonora (2019). Phase Transformations within the Cu-Pd-Sn system.
• 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.
• 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..
• Sunding, Martin Fleissner; Løberg, Monika; S. Azar, Amin; Stange, Marit Synnøve Sæverud; Almeida Carvalho, Patricia; Karlsen, Ole Bjørn; Pike, Nicholas; Gunnæs, Anette Eleonora; Diplas, Spyridon & Løvvik, Ole Martin (2019). The Need for a Multi-Technique Approach in the Search for New Phase-Transforming Materials. Show summary

  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).

• Løberg, Monika; Løvvik, Ole Martin & Gunnæs, Anette Eleonora (2018). Energy Conversion using Phase Transforming Materials - the Cu-Pd-Sn system.
• Løberg, Monika; Løvvik, Ole Martin & Gunnæs, Anette Eleonora (2018). Martensitic like phase transformations in the Cu-Pd-Sn system.
• Løberg, Monika & Gunnæs, Anette Eleonora (2017). Influence of Mn Stoichiometry on the Structure and Thermoelectric Properties of CaMn(1+y)O(3-d). Show summary

  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).

View all works in Cristin