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Electrical transport and thermoelectric properties of Y1-x Cax Co O3 (0≤x≤0.1) at high temperatures

Journal of Applied Physics, ISSN: 0021-8979, Vol: 101, Issue: 8
2007
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  • Citations
    15
    • Citation Indexes
      15
  • Captures
    11

Conference Paper Description

The effects of Ca substitution for Y on the electrical transport and thermoelectric properties of Y1-x Cax Co O3 (0≤x≤0.1), prepared by using the sol-gel process, were investigated in the temperature range from 300 to 780 K. The results indicated that direct current electrical resistivity ρ of Y1-x Cax Co O3 decreased remarkably with increasing Ca content x as x≤0.01, which could mainly be attributed to the increase of hole concentration due to substitution of Ca2+ for Y3+. The temperature dependences of the resistivity for Y1-x Cax Co O3 were all found to be basically consistent with small-polaron hopping conduction model. Although Seebeck coefficient S of Y1-x Cax Co O3 at low temperatures T<∼550 K decreased remarkably with increasing x, it approached a limit value ∼150 μVK at ∼800 K for all the samples with different x, which was consistent well with the thermopower resulting from the degeneracy of electron configuration estimated from Heikes formula by assuming that Co3+ and Co4+ exist in low spin state. Experiments showed that thermal conductivity κ of Y1-x Cax Co O3 came mainly from its lattice component, whose decrease with increasing x could be chiefly ascribed to impurity-scattering effect due to Ca doping. The thermoelectric figure of merit ZT (= S2 Tρ κ) of Y1-x Cax Co O3 changed nonmonotonously with increasing doping content of Ca, and Y0.95 Ca0.05 Co O3 was found to have optimum thermoelectric properties with ZT=0.019 at 660 K, which was about ten-fold greater than that of YCo O3, indicating that its thermoelectric properties could be improved effectively by appropriate substitution of Ca for Y in this compound. © 2007 American Institute of Physics.

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