Google Search

A7: Developments in measurement techniques and preparation methods

Thermoelectric properties of p-type Bi2Sr2Co2Ox bulks prepared by a partial melting method followed by a hot pressing process

Emmanuel Combe1, Ryoji Funahashi1, Feridoon Azough2, Tristan Barbier1, Robert Freer2
1AIST Kansai, Osaka, Japan2School of Materials, Univ. of Manchester, United Kingdom

Misfit cobaltites are promising materials for thermoelectric applications at high temperature in air. A ZT value of about 0.2 at 973 K in air has been measured for Bi2Sr2Co2Ox polycrystalline materials [1]. Bi2Sr2Co2Ox (BSC-222 phase) exhibits a layered structure where conducting CoO2 and insulating Bi2Sr2O4 layers alternate along the c-axis with a misfit structure [2]. By the way, a decrease of the thermal conductivity through phonon scattering at the interface between layers is expected to occur.

For widespread large-scale use of this material, a significant increase of the thermoelectric performances is required. The enhancement of the material density, the improvement of grain alignment and the increase of the average grain size are usually investigated in order to decrease scattering of electron carriers at grain boundaries. However, the thermal conductivity of such prepared bulks is also increased. For simultaneously decrease the electrical resistivity and thermal conductivity, an appropriate microstructure must be prepared.

We recently investigated the use of hot pressing or partial melting processing ways for preparing BSC-222 bulks with high density and improved grain alignment or large grain size, respectively [3]. The electrical resistivity and thermal conductivity can be decreased simultaneously in partial melted samples. These samples have simultaneously large average grain size and appropriate bulk density. For reaching higher thermoelectric performances, the grain alignment must be also considered. By single partial melting process, it is not possible to obtain well aligned grains. Applying pressure during preparation of BSC-222 samples is necessary. By combining partial melting and hot pressing processing techniques successively, high performed BSC-222 bulks are expected to be prepared.

  

 

[1] R. Funahashi, I. Matsubara, S. Sodeoka, Appl. Phys. Letters 76 [17] (2000) 2385

[2] H. Leligny, D. Grebille, et al., Acta Cryst. Sect. B, 56 (2000) 173

[3] E. Combe, R. Funahashi et al., submitted