Impact of Thermochemical Treatments on Electrical Conductivity of Donor-Doped Strontium Titanate Sr(Ln)TiO₃ Ceramics

abstract

The remarkable stability, suitable thermomechanical characteristics, and acceptable electrical properties of donor-doped strontium titanates make them attractive materials for fuel electrodes, interconnects, and supports of solid oxide fuel and electrolysis cells (SOFC/SOEC). The present study addresses the impact of processing and thermochemical treatment conditions on the electrical conductivity of SrTiO3-derived ceramics with moderate acceptor-type substitution in a strontium sublattice. A-site-deficient Sr0.85La0.10TiO3-delta and cation-stoichiometric Sr0.85Pr0.15TiO3+delta ceramics with varying microstructures and levels of reduction have been prepared and characterized by XRD, SEM, TGA, and electrical conductivity measurements under reducing conditions. The analysis of the collected data suggested that the reduction process of dense donor-doped SrTiO3 ceramics is limited by sluggish oxygen diffusion in the crystal lattice even at temperatures as high as 1300 degrees C. A higher degree of reduction and higher electrical conductivity can be obtained for porous structures under similar thermochemical treatment conditions. Metallic-like conductivity in dense reduced Sr0.85La0.10TiO3-delta corresponds to the state quenched from the processing temperature and is proportional to the concentration of Ti3+ in the lattice. Due to poor oxygen diffusivity in the bulk, dense Sr0.85La0.10TiO3-delta ceramics remain redox inactive and maintain a high level of conductivity under reducing conditions at temperatures below 1000 degrees C. While the behavior and properties of dense reduced Sr0.85Pr0.15TiO3+delta ceramics with a large grain size (10-40 mu m) were found to be similar, decreasing grain size down to 1-3 mu m results in an increasing role of resistive grain boundaries which, regardless of the degree of reduction, determine the semiconducting behavior and lower total electrical conductivity of fine-grained Sr0.85Pr0.15TiO3+delta ceramics. Oxidized porous Sr0.85Pr0.15TiO3+delta ceramics exhibit faster kinetics of reduction compared to the Sr0.85La0.10TiO3-delta counterpart at temperatures below 1000 degrees C, whereas equilibration kinetics of porous Sr0.85La0.10TiO3-delta structures can be facilitated by reductive pre-treatments at elevated temperatures.

keywords

OXIDE FUEL-CELLS; ELECTROCHEMICAL PERFORMANCE; ELECTRONIC TRANSPORT; ANODE MATERIALS; PEROVSKITE; BEHAVIOR; SRTIO3; TEMPERATURE; LA; INTERCONNECT

subject category

Chemistry; Materials Science; Metallurgy & Metallurgical Engineering; Physics

authors

Bamburov, A; Kravchenko, E; Yaremchenko, AA

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)

acknowledgements

This work was developed within the scope of the PhD project of A.B. supported by the FCT (grant SFRH/BD/150704/2020), and the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (https://doi.org/10.54499/UIDB/50011/2020), UIDP/50011/2020 (https://doi.org/10.54499/UIDP/50011/2020), and LA/P/0006/2020 (https://doi.org/10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC).