Unlocking the potential of a caged star: Thermoelectric quaternary clathrates
Doctoral thesis, 2021

Heat losses are an inevitable consequence of any energy conversion process, dictated by the second law of thermodynamics.
This not only leads to an eternal struggle, via the pursuit of maximal efficiency, it also undermines our efforts to solve the two issues that pose the most significant challenges to modern society: climate change and the worlds surging energy need. Thanks to our inherent ingenuity, humankind has, however, been adept at finding ways of harnessing the power of heat; from the fires that lit up the neolithic era to the steam engines of the industrial revolution. Thermoelectrics can, in some sense, be seen as the next step in this endeavour, since they allow the direct conversion of a temperature difference to an electric voltage.

This thesis summarises a seven year long journey, which has focused on a fascinating and unique group of thermoelectric materials, namely inorganic clathrates. Though these have been the subject of intense research over the last three decades, many of their properties and attributes have, as of yet, not been fully explored. In particular, this project has addressed three fundamental questions: (i) Why is the lattice thermal conductivity intrinsically low? (ii) What is the impact of chemical ordering on the physical properties? (iii) How can the electronic transport be optimised?

Due to the inherent complexity of these materials, computational and experimental methods should ideally be used in tandem, in order to gain further insights. This project has, thus, involved the use of both atomic scale simulations, based on a combination of density functional theory, alloy cluster expansions, and Monte Carlo simulations, as well as advanced measurement and characterisation techniques. Through these efforts, the confusion regarding the origin of the low lattice thermal conductivity has partly been clarified. In addition, it has been shown that chemical ordering in these materials leads to the emergence of an order-disorder transition, which has a direct impact on the physical properties. Last but not least, it is found that the consideration of ternary systems can facilitate the enhancement of the thermoelectric performance by enabling not only independent tuning of doping level and band structure via the composition, but also manipulation of the nano- and microstructure.

Inorganic clathrates

Boltzmann Transport

Monte Carlo


Cluster expansion

Venue: 10-an, Research house 1, Chemistry building [Online: password can be obtained upon request]
Opponent: Ole Martin Løvvik, Adjunct Professor, Department of Physics, University of Oslo


Joakim Brorsson

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry

Order-Disorder Transition in Inorganic Clathrates Controls Electrical Transport Properties

Chemistry of Materials,; Vol. 33(2021)p. 4500-4509

Journal article

Zhang, Y., Brorsson, J., Kamiyama, T., Saito, T., Erhart, P., Palmqvist E. C. Investigating the chemical ordering in quaternary clathrate Ba8AlxGa16–xGe30

Brorsson, J., Hashemi, A., Fan, Z., Fransson, E., Eriksson, F., Ala-Nissila, T., Krasheninnikov, A. V., Komsa, H.-P., Erhart, P. Efficient calculation of the lattice thermal conductivity by atomistic simulations with ab-initio accuracy

Brorsson, J., Palmqvist E. C., Erhart, P. Strategic optimization of the electronic transport properties of pseudo-ternary clathrates

Zhang, Y., Brorsson, J., Qiu, R., Erhart, P., Palmqvist E. C. Effect of Al/Ga ratio on atomic vacancies content and thermoelectric properties in clathrates Ba8AlxGa16–xGe30

Brorsson, J., Palmqvist E. C., Erhart, P. First-principles study of order-disorder transitions in pseudo-binary clathrates

En av de viktigaste och kanske svåraste frågor som mänskligheten ställts inför är hur vi skall kunna tillfredställa världens ökande energibehov på ett sätt som är långsiktigt hållbart. Trots att alla processer leder till energiförluster, vilket kan ses som boven i detta drama, så har människan genom tiderna kommit på alltmer innovativa sätt att ta vara på kraften i den värme som därmed alstras. Upptäckten av den termoelektriska effekten, som gör det möjligt att direkt omvandla en temperaturskillnad till elektricitet, kan ses som ett steg i denna utveckling. En typ av material som lämpar sig för sådana tillämpningar är oorganiska klatrater. Dessa uppmärksammades under tidigt 90-tal på grund av deras låga termiska ledningsförmåga samt unika atomstruktur som består av ett nätverk med "värdatomer" vars hålrum bebos av "gästatomer".

Mycket av forskningen kring termoelektriska klatrater har syftat till att utröna sambandet mellan de termoeletriska egenskaperna och värdatomernas fördelning i materialet, vilket motsvarar graden av kemisk ordning, samt interaktioner med gästatomerna. Målet med mitt arbete, som bygger på en kombination av experimentella studier samt datorberäkningar baserade på maskininlärning, har specifikt varit att finna svar på tre fundamentala frågor rörande klatrater: (i) Vad är orsaken till den låga termiska ledningsförmågan? (ii) På vilket sätt påverkas de fysiska egenskaperna av den kemiska ordningen? (iii) Hur kan de elektriska egenskaperna optimeras?

Subject Categories

Inorganic Chemistry

Materials Chemistry

Theoretical Chemistry

Condensed Matter Physics

Driving Forces

Sustainable development

Innovation and entrepreneurship


Basic sciences


C3SE (Chalmers Centre for Computational Science and Engineering)

Chalmers Materials Analysis Laboratory

Areas of Advance

Materials Science



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4998



Venue: 10-an, Research house 1, Chemistry building [Online: password can be obtained upon request]


Opponent: Ole Martin Løvvik, Adjunct Professor, Department of Physics, University of Oslo

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