Effects of preferred orientation and crystal size on thermoelectric properties of sodium cobalt oxide

Yin Wu, Jun Wang, Xinba Yaer, Lei Miao, Boyu Zhang, Feng Guo, Shuai Zhang

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


To examine the effect of crystal size and orientation effect on ZT, polycrystalline NaxCo2O4 materials were prepared by pressing layered crystals obtained in sol-gel (SG) synthesis, molten salt synthesis (MSS) with and without additional ball milling (BM) treatment and 1:1 molar ratio mixture (Mixture) of BM powder and MSS powders. We found that the orientation effect and crystal size for four samples follow Mixture < SG < BM < MSS and BM < Mixture < SG < MSS, respectively. Electrical conductivity was obviously enhanced in the highly orientated BM and MSS samples when compared with SG and Mixture. It appears that the crystal size plays a dominant role in thermal conductivity rather than Seebeck coefficient by controlling the phonon scattering at grain boundaries. Thermal conductivity for BM was significantly decreased in comparison to MSS, although both BM and MSS show comparable orientation effect. The maximum ZT value is developed to near 0.51 at 814K upon increasing the electrical resistivity and decreasing the thermal conductivity, which are mainly governed by the condition of crystal size and orientation effect.

Original languageEnglish
Article number1650010
JournalFunctional Materials Letters
Issue number1
Publication statusPublished - 2016 Feb 1
Externally publishedYes


  • Thermoelectric
  • molten salt synthesis
  • preferred orientation
  • sodium cobalt oxide
  • sol-gel method

ASJC Scopus subject areas

  • Materials Science(all)


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