Broadening the temperature range for high thermoelectric performance of bulk polycrystalline strontium titanate by controlling the electronic transport properties

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 6; no. 28; pp. 7594 - 7603
• Main Authors: Li, Jian-Bo, Wang, Jun, Li, Jing-Feng, Li, Yan, Yang, He, Yu, Hao-Yang, Ma, Xiao-Bo, Yaer, Xinba, Liu, Liang, Miao, Lei
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Doping; Electron transport; Figure of merit; Niobium carbide; Point defects; Polycrystals; Power factor; Scattering; Sintering (powder metallurgy); Strontium titanates; Temperature; Thermoelectric materials; Titanium dioxide; Transport properties
• DOI: 10.1039/C8TC02130A
• ISSN: 2050-7526

Strontium titanate (SrTiO 3 ) is a promising n-type thermoelectric material at high temperature. However, to date, its reported high dimensional figure of merit ( zT ) > 0.4 has only been achieved in a narrow temperature range near 1000 K. In this study, zT values of >0.4 were achieved in the broad temperature range of 769–1009 K in bulk SrTiO 3 co-doped with La and Nb with in situ precipitation of second phases of NbC and TiO 2−δ . The electronic transport properties of the samples were optimized by adjusting the doping ratio, resulting in a large power factor of 1.82 mW m −1 K −2 at 622 K for 7 mol% La–7 mol% Nb-doped SrTiO 3 . Notably, the power factor (PF) decreased more gradually with increasing temperature, resulting in a high PF of 1.28 mW m −1 K −2 even at 1009 K. In addition, precipitation of the second phases occurred during sintering of the mixture of La–Nb doped SrTiO 3 nano powder and carbon powder, which provided additional phonon scattering centers except for the phonon scattering centers of La and Nb point defects. This high thermoelectric performance achieved over a broad temperature range could be beneficial for broadening the range of application temperatures for bulk polycrystalline SrTiO 3 . Furthermore, the tailoring strategy of co-doping, an in situ second phase, and oxygen vacancies applied in this study may be applicable to other oxide thermoelectric materials.