Reduced thermal conductivity in niobium-doped calcium-manganate compounds for thermoelectric applications

Reduction of thermal conductivity is essential for obtaining high energy conversion efficiency in thermoelectric materials. We report on significant reduction of thermal conductivity in niobium-doped CaO(CaMnO₃)m compounds for thermoelectric energy harvesting due to introduction of extra CaO-planes in the CaMnO₃-base material. We measure the thermal conductivities of the different compounds applying the laser flash analysis at temperatures between 300 and 1000K, and observe a remarkable reduction in thermal conductivity with increasing CaO-planar density, from a value of 3.7W·m^-1K^-1 for m =∞ down to 1.5W·m^-1K^-1 for m = 1 at 400 K. This apparent correlation between thermal conductivity and CaO-planar density is elucidated in terms of boundary phonon scattering, providing us with a practical way to manipulate lattice thermal conductivity via microstructural modifications.