Improved Thermoelectric Properties of SrTiO3 via (La, Dy and N) Co-Doping: DFT Approach

Pornsawan Sikam; Ruhan Thirayatorn; Thanayut Kaewmaraya; Prasit Thongbai; Pairot Moontragoon; Zoran Ikonic

doi:10.3390/molecules27227923

Improved Thermoelectric Properties of SrTiO₃ via (La, Dy and N) Co-Doping: DFT Approach

Molecules. 2022 Nov 16;27(22):7923. doi: 10.3390/molecules27227923.

Authors

Pornsawan Sikam^{1

2}, Ruhan Thirayatorn³, Thanayut Kaewmaraya^{3

4}, Prasit Thongbai^{3

4}, Pairot Moontragoon^{3

4

5}, Zoran Ikonic⁶

Affiliations

¹ Research Center for Quantum Technology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
² Office of Research Administration, Chiang Mai University, Chiang Mai 50200, Thailand.
³ Department of Physics, Khon Kaen University, Khon Kaen 40002, Thailand.
⁴ Institute of Nanomaterials Research and Innovation for Energy (IN-RIE), Research Network of NANOTEC-KKU (RNN), Khon Kaen University, Khon Kaen 40002, Thailand.
⁵ Thailand Center of Excellence in Physics, Commission on Higher Education, Bangkok 10400, Thailand.
⁶ School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK.

Abstract

This work considers the enhancement of the thermoelectric figure of merit, ZT, of SrTiO₃ (STO) semiconductors by (La, Dy and N) co-doping. We have focused on SrTiO₃ because it is a semiconductor with a high Seebeck coefficient compared to that of metals. It is expected that SrTiO₃ can provide a high power factor, because the capability of converting heat into electricity is proportional to the Seebeck coefficient squared. This research aims to improve the thermoelectric performance of SrTiO₃ by replacing host atoms by La, Dy and N atoms based on a theoretical approach performed with the Vienna Ab Initio Simulation Package (VASP) code. Here, undoped SrTiO₃, Sr_0.875La_0.125TiO₃, Sr_0.875Dy_0.125TiO₃, SrTiO_2.958N_0.042, Sr_0.750La_0.125Dy_0.125TiO₃ and Sr_0.875La_0.125TiO_2.958N_0.042 are studied to investigate the influence of La, Dy and N doping on the thermoelectric properties of the SrTiO₃ semiconductor. The undoped and La-, Dy- and N-doped STO structures are optimized. Next, the density of states (DOS), band structures, Seebeck coefficient, electrical conductivity per relaxation time, thermal conductivity per relaxation time and figure of merit (ZT) of all the doped systems are studied. From first-principles calculations, STO exhibits a high Seebeck coefficient and high figure of merit. However, metal and nonmetal doping, i.e., (La, N) co-doping, can generate a figure of merit higher than that of undoped STO. Interestingly, La, Dy and N doping can significantly shift the Fermi level and change the DOS of SrTiO₃ around the Fermi level, leading to very different thermoelectric properties than those of undoped SrTiO₃. All doped systems considered here show greater electrical conductivity per relaxation time than undoped STO. In particular, (La, N) co-doped STO exhibits the highest ZT of 0.79 at 300 K, and still a high value of 0.77 at 1000 K, as well as high electrical conductivity per relaxation time. This renders it a viable candidate for high-temperature applications.

Keywords: SrTiO3; rare-earth doping; thermoelectric properties.

Grants and funding

N42A650294/National Research Council of Thailand (NRCT) and Khon Kaen University