ICT2014 Abstracts

In CoSb₃ skutterudites, the thermal conductivity can be reduced prominently by filling the intrinsic crystal voids of CoSb₃ skutterudites with various filler atoms that have heavy atomic mass and small radius. Likewise, the electrical conductivity and thermopower are typically “tuned” via doping on the Cobalt (Co) and/or Antimony (Sb) sites. To either effect, the thermoelectric (TE) performance is hence manipulated in an effort to create a more efficient thermoelectric (TE) material. However, there exists a limit to which the skutterudite crystal structure can maintain stability with doping foreign elements.  This limit is known as the filling fraction limit (FFL) which is the best known theoretical, or experimental, doping limit for intrinsic voids in crystals (theoretical and experimental FFL’s may vary).  The FFL of a doping element into a skutterudite material is typically defined by an element’s ionic radius, electronegativity and valence states. Reports verify that exceeding this FFL can lead to in situ nano-sized secondary phases, which have also proven to lower lattice thermal conductivity as well as positively affecting the electrical properties.  Here, we report our result of exceeding the FFL of Pr (FFL (theoretical) = 0.07) in CoSb₃ skutterudites. We observe an unusual behavior in thermopower for samples with 0.02 < y < 0.15. The Power factor of reported samples was improved from 0.1 Wm^-1K^-1 to 2.5 Wm^-1K^-1at 775K.  Total thermal conductivity was reduced from 4.5 Wm^-1K^-1 to 2.5 Wm^-1K^-1 at 775K.These enhancements in both electrical and thermal properties leads to overall increase in ZT. Further investigations of thermal transport, electronic transport and microstructure suggest that the in-situ Pr-contained secondary phases that were formed while filling fraction of Pr is increased would be the main donors of electrons that result in the high electric conductivity and also the scattering centers for phonons that result in the low thermal conductivity. This approach provides an effective way to improve the TE performance of Pr filled CoSb₃ skutterudites; it may also have the potential of being investigated in other single filled CoSb₃ skutterudites.