High thermoelectric performance in donor-substituted strontium titanate-based composites processed by laser floating zone

abstract

Oxide thermoelectrics, made from abundant, eco-friendly materials, can withstand high-temperature gradients, making them highly promising for high-temperature waste heat harvesting. Recent advancements in the efficiency of thermoelectric material families have been driven by composite approaches, fostering synergistic effects between materials, further enhanced by advanced processing techniques. Accordingly, this study explores the design of oxide-based thermoelectric composites, involving the redistribution of a common substituting cation between composite phases, driven by laser floating zone (LFZ) processing. Niobium substituted strontium titanate/rutile composite material with a nominal composition Sr0.97Ti0.8Nb0.2O3 / 0.15Ti(0.95)Nb(0.05)O(2) was processed by LFZ at various pulling rates (50, 100, and 200 mm/h), followed by post-thermal treatment under highly reducing conditions. The obtained samples showed inhomogeneous niobium distribution between perovskite and rutile phases shaped by strongly non-equilibrium conditions inherent to the LFZ processing, in contrast to the conventional solid-state route. Adjusting the pulling rate enabled a certain degree of control over niobium incorporation into both phases. Primarily driven by an enhanced Seebeck coefficient, the LFZ-processed and thermally treated samples demonstrated high power factors, reaching 1350-820 mu WK-2m(-1) at 473-1173 K, respectively. An appealing ZT of 0.52 at 1173 K was achieved for the composite sample processed at 100 mm/h and subjected to thermal treatment. This performance is attributed to a combination of a high power factor and low thermal conductivity (similar to 2 Wm(-1)K-1 at 1173 K), enabled by phase and compositional inhomogeneities, as well as residual porosity introduced by LFZ processing. The LFZ technique offers considerable potential for optimisation and has proven to be a powerful tool for designing ceramic composite thermoelectric materials.

keywords

SRTIO3 CERAMICS; TEMPERATURE; OXIDE; NB; CA3CO4O9; PROGRESS; GROWTH; DEFECT

subject category

Chemistry; Materials Science; Metallurgy & Metallurgical Engineering

authors

Lopes, D; Vieira, MA; Ferreira, NM; Shvartsman, VV; Dura, OJ; Batista, FQ; Salak, AN; Mikhalev, S; Costa, F; Kovalevsky, A

Groups

G3 - Electrochemical Materials, Interfaces and Coatings

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

Phase transitions and morphotropic phase boundary in bismuth-containing oxides with perovskite structure synthesized under high pressure: a search for lead-free piezoelectric materials. (PZT-Free)

acknowledgements

This work was developed within the scope of the project i3N, LA/P/0037/2020, UIDB/50025/2020 & UIDP/50025/2020, financed by national funds through the FCT/MEC. The authors also acknowledge the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020) , UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020) , financed by national funds through the FCT/MCTES (PIDDAC) . Diogo Lopes acknowledges the PhD scholarship by FCT (grant https://d oi.org/10.54499/2020.06454.BD) . Miguel Vieira acknowledges the PhD scholarship by FCT (grant 2022.12347.BD) . D.L., V.V.S., and A.N.S acknowledge the support of the bilateral Portugal-Germany (FCTDAAD) project PZT-FREE (grants 2021.09702.CBM and 57610755, respectively) . S.M acknowledges the support of the projects UIDB/00481/2020 and UIDP/00481/2020-Fundacao para a Ciencia e a Tecnologia, DOI 10.54499/UIDB/00481/2020 (https://doi.org/10.544 99/UIDB/00481/2020) and DOI 10.54499/UIDP/00481/2020 (https://doi.org/10.54499/UIDP/00481/2020) . This work was also funded by national funds (OE) , through FCT-Fundacao para a Ciencia e a Tecnologia, I.P., in the scope of the