Influence of Zr-doping on the structure and transport properties of rare earth high-entropy oxides
Mohana V Kante,
Ajai R Lakshmi Nilayam,
Kosova Kreka,
Horst Hahn,
Subramshu S Bhattacharya,
Leonardo Velasco,
Albert Tarancón,
Christian Kübel,
Simon Schweidler,
Miriam Botros
Affiliations
Mohana V Kante
Institute of Nanotechnology, Karlsruhe Institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany
Ajai R Lakshmi Nilayam
Institute of Nanotechnology, Karlsruhe Institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany; Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany
Department of Advanced Materials for Energy, Catalonia Institute for Energy Research-IREC , Barcelona, Spain
Horst Hahn
Institute of Nanotechnology, Karlsruhe Institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany; The University of Oklahoma, School of Sustainable Chemical, Biological and Materials Engineering , 100 E. Boyd St., Norman, OK 73019, United States of America
Subramshu S Bhattacharya
Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras , Chennai 600036, India
Leonardo Velasco
Universidad Nacional de Colombia sede de La Paz , Km 9 via Valledupar—La Paz, 202010 Cesar, Colombia
Department of Advanced Materials for Energy, Catalonia Institute for Energy Research-IREC , Barcelona, Spain; Catalan Institution for Research and Advanced Studies (ICREA) , Barcelona, Spain
Christian Kübel
Institute of Nanotechnology, Karlsruhe Institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany; Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany
Simon Schweidler
Institute of Nanotechnology, Karlsruhe Institute of Technology , Kaiserstraße 12, 76131 Karlsruhe, Germany
Fluorite-type ceria-based ceramics are well established as oxygen ion conductors due to their high conductivity, superseding state-of-the-art electrolytes such as yttria-stabilized zirconia. However, at a specific temperature and oxygen partial pressure they occasionally exhibit electronic conduction attributed to polaron hopping via multivalent cations (e.g. Pr and Ce). (Ce, La, Pr, Sm, Y)O _2− _δ is a high-entropy oxide with a fluorite-type structure, featuring low concentrations of multivalent cations that could potentially mitigate polaron hopping. However, (Ce, La, Pr, Sm, Y)O _2− _δ undergoes a structural transition to the bixbyite-type structure above 1000 °C. In this study, we introduce Zr doping into (Ce, La, Pr, Sm, Y)O _2− _δ to hinder the structural transition at elevated temperatures. Indeed, the fluorite structure at elevated temperatures is stabilized at approximately 10 at.% Zr doping. The total conductivity initially increases with doping, peaking at 5 at.% Zr doping, and subsequently decreases with further doping. Interestingly, electronic conductivity in (Ce, La, Pr, Sm, Y) _1− _x Zr _x O _2− _δ under oxidizing atmospheres is not significant and is lowest at 8 at.% Zr. These results suggest that ceria-based high-entropy oxides can serve as oxygen ion conductors with a significantly reduced electronic contribution. This work paves the way for new compositionally complex electrolytes as well as protective coatings for solid oxide fuel cells.
