Large anisotropic thermoelectricity in perovskite related layered structure: SrnNbnO3n+2 (n=4,5)

We measured the thermal and charge transport properties of perovskite-related layered structures. Strontium-Niobates, which were expressed as SrnNbnO3n+2 (n=4: Sr1.8La0.2Nb2O7, n=5: Sr5Nb5O17), to explore their thermoelectricities and thermal anisotropies. The behaviors of the thermoelectric parameters (thermal conductivity, Seebeck coefficient, resistivity) were strongly anisotropic in all crystallographic axes (a, b, and c) and large anisotropy exists even in the in-plane direction of the layered structure. Especially, along the a-axis in which corner-sharing NbO6 octahedra aligned straightly, contrastive properties were observed between Sr1.8La0.2Nb2O7 and Sr5Nb5O17. For Sr1.8La0.2Nb2O7, a thermally activated charge conduction is pronounced in the temperature dependence of Seebeck coefficient and resistivity, on the other hand, it was a metallic nature for Sr5Nb5O17. In both compounds, ZT results in anisotropic due to the anisotropic properties of thermoelectric parameters, the best performance is commonly observed in the a-axis. The respective ZT values at room temperature are 3.5 X 10(-2) and 3.6 X 10(-3). (C) 2010 American Institute of Physics. [doi:10.1063/1.3510585]