Transport properties of high entropy perovskite ceramics for thermoelectric application Konrad Kuc, Daniel Jaworski, Maria Gazda, Tadeusz Miruszewski Institute of Nanotechnology and Materials Engineering, Gdańsk University of Technology, Narutowicza 11/12, 80-233 Gdańsk, Poland Multicomponent oxides (MO) usually contain five or more elements occupying the same crystallographic position [1] . The lattice distortions influence not only the mechanical but also the transport properties of MO materials. In consequence, the electrical and thermoelectric properties, strongly depend on the structural properties [2,3]. Mixed ionic and electronic conductors (MIEC) conduct both mobile ions (oxygen ions or protonic defects) and electrons/holes. Triple-conducting oxides belong to MIEC, however, they are characterized by charge carriers - electrons, protons, and oxygen ions. Cubic perovskites containing both acceptor-type constituents, as well as transition metals, were shown to be promising triple-conducting oxides [4] . In this work, high entropy oxides with perovskite structure and nominal formula Ba(TiFeCoYZrSnCeHf) 0.125 O 3-δ (M1) and Ba(TiFeCoYZrSnCeHfBi) 0.11 O 3-δ (M2) were prepared by conventional solid-state reaction route. The crystal structure of ceramics was studied using the XRD method and the results showed a single perovskite phase in both samples. The electrical transport studies showed different total electrical conductivity values in dry and humidified air at lower temperatures. The conductivity of M1 was in the range of 1.6·10 -3 to 2.3·10 -2 Scm -1 while that of M2 was 1.3·10 -3 to 2.7·10 -2 Scm -1 . Seebeck coefficient measurements in a dry atmosphere showed a maximum value of 245 µV/K at 354◦C and 193 µV/K at 796 ◦C for M1 and M2, respectively. A small polaron transport in the M1 sample was assumed according to the Seebeck temperature dependence [5] and activation energy for the thermal transport of electrons which was 0,22 and 0,18 eV for dry and humidified air, respectively. The electrical conductivity relaxation (ECR) method allowed for the determination of the surface exchange coefficients k and chemical diffusivity D related to oxygen transport [6] . The exemplary results showed that for the M1 materialchemical diffusivity of oxygen at 600, 650, and 700 ◦ C was in a range from 9.7.10 -4 to 2.6.10 -2 cm 2 s -1 and for the M2 sample from 5.8.10 -2 to 2.7.10 -3 cm 2 s -1 . What is more, the chemical diffusion coefficients obtained for the dry atmosphere were higher than in the humidified one in both samples, which indicates that protonic defects present in the material affect oxygen transport. References 1. H. Li, Y. Zhou, Z. Liang, H. Ning, X. Fu, Z. Xu, T. Qiu, W. Xu, R. Yao, J. Peng, Coatings 11 (2021) 628. 2. A. Sarkar, Q. Wang, A. Schiele, M.R. Chellali, S.S. Bhattacharya, D. Wang, T. Brezesinski, H. Hahn, L. Velasco, B. Breitung, Adv. Mater. 31 (2019) 1806236. 3. K. Chen, X. Pei, L. Tang, H. Cheng, Z. Li, C. Li, X. Zhang, L. An, Journal of the European Ceramic Society 38 (2018) 4161–4164. 4. D. Poetzsch, R. Merkle, J. Maier, Faraday Discuss. 182 (2015) 129–143. 5. Y. Natanzon, A. Azulay, Y. Amouyal, Isr. J. Chem. 60 (2020) 768–786. 6. B.T. Na, T. Yang, J. Liu, S. Lee, H. Abernathy, T. Kalapos, G. Hackett, Solid State Ionics 361 (2021) 115561.
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