Ionic transport properties of nanocrystalline high entropy oxides

本方案的主要科学目标是研究两类新型材料的离子输运：高熵氧化物(HEO)-Li+离子在具有相纯岩盐结构的过渡金属基R-HEO中沿阳离子亚晶格的输运，以及氧离子在具有相纯萤石结构的稀土基F-HEO中的阴离子亚晶格输运。预计我们在离子传输特性方面的合作将为了解这种新型氧化物材料的结构和功能特性做出有价值的贡献，并帮助探索这种新型氧化物材料的全部潜力。在印度合作机构IIT Madras制备的粉末和陶瓷的微观结构将在卡尔斯鲁厄理工学院纳米技术研究所(INT)使用X射线衍射、扫描电子显微镜、透射电子显微镜和EXAFS进行表征。随后，将使用电化学阻抗谱(EIS)分析在环境温度附近的温度范围内Li+离子迁移的情况下的电化学性质，以及在高温下O2-离子迁移的情况下。在离子输运基础研究的基础上，我们将利用HEO材料组装和表征半锂离子电池和固体氧化物燃料电池(SOFC)。此外，还将使用核磁共振来测定锂离子的扩散系数，并使用拉曼光谱来检测HEO中的缺陷化学。该工作计划建立在德国和印度首席研究人员(PI)之间长达20年的纳米陶瓷合作以及过去三年来他们在HEO新领域的开创性合作工作的基础上。这两个小组的优势被很好地结合在拟议的联合研究工作中。在IIT Madras，印度PI的研究重点是合成、加工和结构表征，在卡尔斯鲁厄理工学院(KIT)纳米技术研究所(INT)，重点在很大程度上是互补的，解决了使用先进技术表征微结构和研究具有应用潜力的功能特性的问题。初步工作--主要由INT和IITM提供的可自由支配资金支持--已经导致了对HEO的一些基本理解，并将在本提案期间以正式方式进一步发展。这两个集团之间的协同作用已经在最近优秀出版物的数量方面得到了明确的确立，其中包括一份《自然通讯》。在科学创新思想和成功合作的证据方面，该提案直接涉及了当前DST-DFG联合呼吁印度-德国在材料科学和工程领域开展合作研究活动的主题。

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.