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Phase stability of ScN-based solid solutions for thermoelectric applications from first-principles calculations
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0003-1785-0864
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 7Article in journal (Refereed) Published
Abstract [en]

We have used first-principles calculations to investigate the trends in mixing thermodynamics of ScN-based solid solutions in the cubic B1 structure. 13 different Sc1−xMxN (M = Y, La, Ti, Zr, Hf, V, Nb, Ta, Gd, Lu, Al, Ga, In) and three different ScN1−xAx (A = P, As, Sb) solid solutions are investigated and their trends for forming disordered or ordered solid solutions or to phase separate are revealed. The results are used to discuss suitable candidate materials for different strategies to reduce the high thermal conductivity in ScN-based systems, a material having otherwise promising thermoelectric properties for medium and high temperature applications. Our results indicate that at a temperature of T = 800 °C, Sc1−xYxN; Sc1−xLaxN; Sc1−xGdxN, Sc1−xGaxN, and Sc1−xInxN; and ScN1−xPx, ScN1−xAsx, and ScN1−xSbx solid solutions have phase separation tendency, and thus, can be used for forming nano-inclusion or superlattices, as they are not intermixing at high temperature. On the other hand, Sc1−xTixN, Sc1−xZrxN, Sc1−xHfxN, and Sc1−xLuxN favor disordered solid solutions at T = 800 °C. Thus, the Sc1−xLuxN system is suggested for a solid solution strategy for phonon scattering as Lu has the same valence as Sc and much larger atomic mass.

Place, publisher, year, edition, pages
American Institute of Physics (AIP) , 2013. Vol. 114, no 7
Keyword [en]
ab initio calculations, aluminium compounds, gadolinium compounds, gallium compounds, hafnium compounds, indium compounds, lanthanum compounds, lutetium alloys, mixing, niobium compounds, nitrogen compounds, phase separation, scandium compounds, solid solutions, superlattices, tantalum compounds, thermal conductivity, thermoelectricity, titanium compounds, vanadium compounds, yttrium compounds, zirconium compounds
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-97662DOI: 10.1063/1.4818415ISI: 000323510900021OAI: oai:DiVA.org:liu-97662DiVA: diva2:649985
Note

Funding Agencies|Swedish Research Council (VR)|621-2009-5258621-2012-4430621-2011-4417|Linnaeus Strong Research Environment LiLi-NFM||Swedish Foundation for Strategic Research||Linkoping Center in Nanoscience and technology (CeNano)||

Available from: 2013-09-19 Created: 2013-09-19 Last updated: 2017-12-06
In thesis
1. Design of Transition-Metal Nitride Thin Films for Thermoelectrics
Open this publication in new window or tab >>Design of Transition-Metal Nitride Thin Films for Thermoelectrics
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermoelectric devices are one of the promising energy harvesting technologies, because of their ability to convert heat (temperature gradient) to electricity by the Seebeck effect. Furthermore, thermoelectric devices can be used for cooling or heating by the inverse effect (Peltier effect). Since this conversion process is clean, with no emission of greenhouse gases during the process, this technology is attractive for recovering waste heat in automobiles or industries into usable electricity. However, the conversion efficiency of such devices is rather low due to fundamental materials limitations manifested through the thermoelectric figure of merit (ZT). Thus, there is high demand on finding materials with high ZT or strategies to improve ZT of materials.

In this thesis, I discuss the basics of thermoelectrics and how to improve ZT of materials, including present-day strategies. Based on these ideas, I propose a new class of materials for thermoelectric applications: transition-metal nitrides, mainly ScN, CrN and their solid solutions. Here, I employed both experimental and theoretical methods to synthesize and study their thermoelectric properties. My study envisages ways for improving the thermoelectric figure of merit of ScN and possible new materials for thermoelectric applications.

The results of my studies show that ScN is a promising thermoelectric material since it exhibits high thermoelectric power factor 2.5x10-3 Wm-1K-2 at 800 K, due to low metallic-like electrical resistivity while retained relatively large Seebeck coefficient. My studies on thermal conductivity of ScN also suggest a possibility to control thermal conductivity by tailoring the microstructure of ScN thin films. Furthermore, my theoretical studies on effects of impurities and stoichiometry on the electronic structure of ScN suggest the possibly to improve ScN ZT by stoichiometry tuning and doping. For CrN and Cr1-xScxN solid solution thin films, the results show that the power factor of CrN (8x10-4 Wm-1K-2 at 770 K) can be retained for the solid solution Cr0.92Sc0.08N. Finally, density functional theory was used to enable a systematic predictionbased strategy for optimizing ScN thermoelectric properties via phase stability of solid solutions. Sc1-xGdxN and Sc1-xLuxN are stabilized as disordered solid solutions, while in the Sc-Nb-N and Sc-Ta-N systems, the inherently layered ternary structures ScNbN2 and ScTaN2 are stable.

Abstract [sv]

Sedan den industriella revolutionen har fossila bränslen varit vår huvudkälla till energi i motorer för transport, elproduktion och uppvärmning av byggnader. Eftersom mänskligheten och vår teknik växer för varje år som går, fortsätter efterfrågan på fossila bränslen att öka. Med tanke på att fossila bränslen inte är förnybara, riskerar vi att de tar slut. Dessutom är resultatet av denna ständiga förbränning av fossila bränslen generering av växthusgaser, t.ex. kolmonoxid och koldioxid, som orsakar klimatförändringar, som ett ytterligare problem. Således finns det ett ökande behov av nya former av energikällor som kan ersätta fossila bränslen.

För närvarande finns det olika typer av tekniker för förnybar energi som solceller, vätgasteknik (bränsleceller), vindkraftverk, vattenkraft, etc. Ett annat koncept som har studerats är energiåtervinning, vilket innebär att fånga eller lagra spillenergi och förvandla det till användbar energi. Spillenergi är den energi, oftast värmeförluster, som förloras i generatorer, vibrationer från motorer, och så vidare. Ungefär 60% av den ursprungliga energin avges som spillvärme. Om vi kan återvinna all denna förlust till användbar energi igen, kan vi spara stora mängder bränslen utsläppen av koldioxid kommer att minska.

Med hänsyn till dessa krav, så är termoelektriska komponenter intressanta kandidater. En termoelektriska komponent är tillverkad av material som direkt återvinner värme (en temperaturgradient) till elektrisk energi utan utsläpp av växthusgaser. De kan också kyla genom den omvända processen, när de genererar en temperaturgradient från en pålagd ström. Detta innebär att de kyler utan rörliga delar eller något kylmedel som kan orsaka miljöproblem. Verkningsgraden är emellertid låg, för närvarande 10% -15%, dessutom är de flesta av dagens termoelektriska material giftiga. Jag har därför studerat en ny klass av material, övergångsmetallnitrider, som en kandidat för termoelektriska tillämpningar. Övergångsmetallnitrider är kända för sina utmärkta mekaniska egenskaper, de används till exempel som beläggningar på skärverktyg i syfte att förbättra prestanda och livslängd. De uppvisar ocksåolika elektriska egenskaper (metaller, halvledare och supraledare). Min studie är inriktad på att förstå de termoelektriska egenskaperna hos övergångsmetallnitrider, främst skandiumnitrid och kromnitrid. Resultaten visar att båda materialen kan vara bra kandidater för termoelektriska tillämpningar.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 178 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1667
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-117760 (URN)10.3384/diss.diva-117760 (DOI)978-91-7519-067-9 (ISBN)
Public defence
2015-06-01, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-05-08 Created: 2015-05-08 Last updated: 2016-08-31Bibliographically approved

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