Relation between structural and thermoelectric properties in chemically stable NaxCoO2 thin films

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Direct conversion of waste heat into electrical energy by thermoelectric modules offers tremendous potential for reducing the overall energy consumption. The efficiency of these devices can be improved by designing “phonon-glass/electron-crystal” materials, which have a high thermopower and electrical conductivity combined with a low thermal conductivity.
Single crystals of NaxCoO2 show very promising thermoelectric properties, however overall performance is limited by a high lattice thermal conductivity. It is expected that this can be improved in NaxCoO2 thin films, due to enhanced phonon scattering. The growth of these thin films is reported, however thermoelectric characterization is very challenging because of chemical instability in air.
We present a method to obtain single-phase NaxCoO2 thin films by pulsed laser
deposition, which are chemically stable in air. Chemical stability of these films is now achieved by the in-situ deposition of an amorphous AlOx capping layer, which prevents reaction of the thin film with moisture and CO2 from air. No degradation of the structural and electrical transport properties of these capped thin films is observed for several months. Subsequently we report a detailed growth study, which results in control over the structural properties of these stable NaxCoO2 thin films. We show that layer thickness, deposition parameters and substrate material can be used to tune the crystalline properties of the thin films. In relation to these structural changes we studied the electrical transport properties and thermopower, demonstrating significantly enhanced thermoelectric potential of these stable NaxCoO2 thin films.
Original languageEnglish
Number of pages1
Publication statusPublished - 24 Jun 2012
EventElectroceramics XIII 2012 - University of Twente, Enschede, Netherlands
Duration: 24 Jun 201227 Jun 2012
Conference number: 13


ConferenceElectroceramics XIII 2012


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