Enhancing the thermoelectric power factor of Sr 0.9 Nd 0.1 TiO 3 through control of the nanostructure and microstructure

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 6; no. 48; pp. 24928 - 24939
• Main Authors: Ekren, Dursun, Azough, Feridoon, Gholinia, Ali, Day, Sarah J., Hernandez-Maldonado, David, Kepaptsoglou, Despoina M., Ramasse, Quentin M., Freer, Robert
• Format: Journal Article
• Language: English
• Published: 11.12.2018
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/C8TA07861K

Donor-doped SrTiO 3 ceramics are very promising n-type oxide thermoelectrics. We show that significant improvements in the thermoelectric power factor can be achieved by control of the nanostructure and microstructure. Using additions of B 2 O 3 and ZrO 2 , high density, high quality Sr 0.9 Nd 0.1 TiO 3 ceramics were synthesised by the mixed oxide route; samples were heat treated in a single step under reducing atmosphere at 1673 K. Synchrotron and electron diffraction studies revealed an I 4/ mcm tetragonal symmetry for all specimens. Microstructure development depended on the ZrO 2 content; low level additions of ZrO 2 (up to 0.3 wt%) led to a uniform grain size with transformation-induced sub-grain boundaries. HRTEM studies showed a high density of dislocations within the grains; the dislocations comprised (100) and (110) edge dislocations with Burger vectors of d (100) and d (110) respectively. Zr doping promoted atomic level homogenization and a uniform distribution of Nd and Sr in the lattice, inducing greatly enhanced carrier mobility. Transport property measurements showed a significant increase in the power factor, mainly resulting from the enhanced electrical conductivity while the Seebeck coefficients were unchanged. In optimised samples a power factor of 2.0 × 10 −3 W m −1 K −2 was obtained at 500 K. This is an ∼30% improvement compared to the highest values reported for SrTiO 3 -based ceramics. The highest ZT value for Sr 0.9 Nd 0.1 TiO 3 was 0.37 at 1015 K. This paper demonstrates the critical importance of controlling the structure at the atomic level and the effectiveness of minor dopants in enhancing the thermoelectric response.