Effect of Mixed Grain Sizes on the Thermoelectric Properties of Ca^sub 0.9^Yb^sub 0.1^MnO3

Issue Title: International Conference on Thermoelectrics 2013. Guest Editors: Jihui Yang, Hiroaki Anno, Matt Beekman, Ryoji Funahashi, Yuri Grin, Emmanuel Guilmeau, Jan Koenig, Bertrand Lenoir, Don Morelli, Lasse Rosendahl, James R. Salvador, Jeff Sharp, David Singh, Tsunehiro Takeuchi, Xiegeng Tang, Chunlei Wang, Hsin Wang, Wenqing Zhang, and Tie-Jun Zhu Ca^sub 0.9^Yb^sub 0.1^MnO3 has been identified as a material that might be suitable for thermoelectric applications. We fabricated micro/nanograined Ca^sub 0.9^Yb^sub 0.1^MnO3 composites, with the aim of controlling the passage of electrons and phonons simultaneously. Micro/nanograined Ca^sub 0.9^Yb^sub 0.1^MnO3 composites containing various fractions of nanosized powder were prepared by sintering mixtures of microparticulate and nanoparticulate Ca^sub 0.9^Yb^sub 0.1^MnO3, obtained by solid-state reaction and by gas-phase reaction, respectively. The electrical resistivity increased markedly when the weight fraction of nanosized powder exceeded 50%, probably as a result of a percolation phenomenon. However, the thermal conductivity was considerably reduced when the weight fraction of nanosized powder exceeded 25%, but then remained almost constant. The absolute values of the Seebeck coefficient of micro/nanograined Ca^sub 0.9^Yb^sub 0.1^MnO3 composites were larger than those of monolithic micro- or nanograin Ca^sub 0.9^Yb^sub 0.1^MnO3, probably as a result of the effects of potential-barrier scattering. The highest dimensionless figure of merit ZT value of 0.09 at 973 K was achieved with a sample containing 50% nanosized powder, and this value is 10% larger than that of monolithic micrograined Ca^sub 0.9^Yb^sub 0.1^MnO3.[PUBLICATION ABSTRACT]