Ionic transport properties of nanocrystalline high entropy oxides

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The primary scientific goal of the present proposal is to investigate the ionic transport along both sublattices in two categories of a novel class of material, high entropy oxides (HEO) – Li+ ion transport along the cation sublattice in transition metal based R-HEO with a phase-pure rock salt structure, and oxygen ion transport along the anion sublattice of rare earth based F-HEO having a phase-pure fluorite structure. It is expected that our collaboration on ionic transport properties will make valuable contributions towards understanding the structure and functional properties and assist in exploring the full potential of the new class of oxide materials.The microstructure of the powders and ceramics prepared at the Indian partner institution IIT Madras will be characterized at the Institute of Nanotechnology (INT) at Karlsruhe Institute of Technology (KIT) using XRD, SEM, TEM and EXAFS. Subsequently, the electrochemical properties will be analyzed using Electrochemical Impedance Spectroscopy (EIS), in case of Li+-ionic transport in a temperature range around ambient temperature, in case of O2—ionic transport at elevated temperatures. Based on the fundamental studies of the ionic transport we will assemble and characterize half and full Li-ion battery cells and Solid Oxide Fuel Cells (SOFC) using HEO materials. NMR will be employed in addition to determine Li-ion diffusivity and Raman spectroscopy to detect the defect chemistry in HEO. The work program builds on a 20-year collaboration on nanocrystalline ceramics between the German and the Indian principal investigators (PI) and their pioneering collaborative work in the new field of HEO over the past three years. The strengths of both groups are well incorporated in the proposed joint research effort. At IIT Madras, the research focus of the Indian PI is on synthesis, processing and structure characterization, at the Institute of Nanotechnology (INT) at Karlsruhe Institute of Technology (KIT) the focus is largely complementary and addresses the characterization of the microstructure using advanced techniques and the study of the functional properties that have potential for applications.The preliminary work - supported largely by discretionary funds available at INT and IITM - has already led to some basic understanding of HEO and will be developed further during this proposal in a formal manner. The synergy between the two groups has been clearly established in terms of the number of recent excellent publications, including one in Nature Communications. In terms of innovative ideas in science and evidence for successful collaboration, the proposal addresses directly the theme of the present DST-DFG joint call for Indo-German collaborative research activities in materials science and engineering.