Grain boundary density on realizing anisotropic thermoelectric properties of Ca3Co4O9-based ceramics with excellent texturation

Abstract

Texturation and anisotropic performance of Ca3Co4O9-based ceramics fabricated by spark plasma sintering were reported, showing promising thermoelectric properties. With template seeds simultaneous additives, the high degree of texturing was obtained. Electrical resistivity decreased from 16.9 to 6.1 mΩ cm and Seebeck coefficient increased from 75.8 to 187.6 μV/K for the sample with 10 wt% templates, which were dominated by a synergistic combination of the grain orientation and grain boundary density. The obvious anisotropic power factors presented, mainly coming from the texturing characteristic. A low total thermal conductivity of 1.16 W/(m·K) were greatly suppressed by tuning broad wavelength phonon scattering, which was ascribed to the layered nanostructures at grain boundaries. Furthermore, the ZT value of 0.31 was obtained at 1073 K for the sample perpendicular to pressure direction, yielding 138 % enhancement compared with that of the other direction. The work confirmed clear evidence that the textured ceramics with template seeds addition have a great influence on thermoelectricity in oxides materials.