Themoelectric properties of Pb and Sr doped Ca3Co4O9 Hiroshi Nakatsugawa1, Hyeon Mook Jeong1, Rak Hee Kim2, Natsuko Gomi1 and Hiroshi Fukutomi1 1 Yokohama National University, Yokohama Japan, E-mail: naka@ynu.ac.jp 2 Changwon National University, Changwon Korea INTRODUCTION EXPERIMENT Since the discovery of large thermoelectric power in the layered compounds NaCo2O4 and Ca3Co4O9, misfit-layered cobalt oxides particularly have attracted much interest as candidates for thermoelectric materials. The Crystal structure of Ca3Co4O9 consists of an alternate stack of a distorted three-layered rock salt (RS) - type Ca2CoO3 block layer (BL) and a CdI2 - type CoO2 conducting sheet parallel to the c-axis. Owing to the size difference between the RS - type BL and the CoO2 sheet, however, the compound has an incommensurate periodicity parallel to the b-axis. Thus the resulting structural formula becomes [Ca2CoO3]pCoO2, where p equals bCoO2 / bCa2CoO3 ～ 0.62. ・conventional solid-state reaction ・electrical resistivity ρ ・Seebeck coefficient S ・thermal conductivity κ ・Hall coefficient RH ・carrier concentration n = 1/eRH ・Hall mobility μ = RH / ρ ・Scanning Electron Microscopy ・neutron powder diffraction (HERMES) ・Rietveld refinement program (PREMOS 91) ・magnetic susceptibility χ Pb2+ Sr2+ Thermoelectric properties x = 0.01 x = 0 x = 0.02 x = 0.03 RWp = 7.4% a = 4.84Å, c = 10.86Å, p = 0.618 RWp = 7.1% a = 4.84Å, c = 10.87Å, p = 0.619 RWp = 8.0% a = 4.84Å, c = 10.89Å, p = 0.617 RWp = 7.2% a = 4.84Å, c = 10.89Å, p = 0.616 Co3.08+ Co3.13+ Co3.14+ Co3.11+ Co3.61+ Co3.61+ Co3.65+ Co3.66+ CONCLUSION ・Seebeck coefficient showed similar large S in all the samples because the substitution of Pb2+ for Ca2+ would keep the carrier (holes) concentration. The Co2 – O3 modulation reveal that Pb ions take Pb2+ in the RS – type BL. ・The magnetic susceptibility reveal that Co1 ions take Co3.1+ and Co2 ions take Co3.6+ in all the samples, which also suggests that Pb ions mainly take Pb2+ in the RS – type BL. ・The maximum ZT is 0.024 in x = 0.02 at RT which resulted from minimum ρ at RT in x = 0.02. J. Sugiyama et al., Phys. Rev. B 68, 134423 (2003)