Combined Theoretical and Experimental Studies of Some Antiperovskite Systems for Energy Applications

Abstract

In recent years there is a significant interest in developing and exploring new and efficient functional materials for emergent energy applications. Such applications include individually tiny energy-consuming device operations but necessarily implemented on a very large volume such as advanced computer chips and sensors for the Internet of Things (IOT), batteries for electric mobility, to grid-scale power handling and storage. Towards this end, in this work, we have focused on two classes of materials, namely antiperovskites and chalcogenides, which are endowed with interesting set of physical properties in view of their unique structures and chemistry. We have chosen two antiperovskites Fe3SnC and Co3CuN as representative cases for battery and spintronic (IOT) applications and the heterostructure interface between antiperovskite nitride (Co3CuN) and perovskite oxide (LaAlO3) as an emerging hetero interface material for its diverse functionality. We have combined theoretical as well as experimental work so as to generate a comprehensive understanding of the basic functionality (structure-chemistry-property relationship) of these materials and how the same unfolds in real applications in each case. In the first chapter, the results of the Fe3SnC system will be presented. In the case of Fe3SnC, the focus has been on lithiation-induced changes in the magnetization and more importantly the Spin Polarization of Fe3SnC. We believe that the outcome of our work on this material suggests that a new approach can be adopted in the form of Iono-Spintronics leading to a spin charge battery wherein lithiation could store spin as well in addition to the charge. We have performed full theoretical first-principles calculations as well as detailed experiments on 1-4 Li incorporated Fe3SnC and have observed very interesting systematic which proves our hypothesis. We show that lithiation-induced structural strains impart changes to the band structure causing major non-monotonic changes in the differential spin-up and spin-down density of states at the Fermi level, namely the spin polarization. 2 In the 2 nd chapter our study focused on nitride-based antiperovskite of Co3CuN, we synthesized a core-shell structure of the form Cu1-xNCo3-y/CuCoFe and examined the same as an anode material for a Li-ion battery or pseudocapacitor A a very high capacity and stability is realized for this new material. Interestingly, while the capacity of the material without the shell is about 408 mAh/g, it is dramatically enhanced to 1150 mAh/g after forming the core-shell structure. In the 3rd chapter, we have addressed the epitaxial heterostructure interface of thin-film between nitride antiperovskite and oxide perovskite by a physical deposition process using the Pulse laser deposition technique (PLD). For the thin film, Co3CuN nitride antiperovskite was used as a target material and single-crystal oxide perovskite LaAlO3 was used as substrate due to their compatibility with the lattice constant. For the first time, using PLD we were able to grow single crystal thin film nitride antiperovskite along the 001 direction of LaAlO3 perovskite substrate. Experimental characterization confirms the phase purity of the same. Thin-film represents an application-worthy platform for this rather unique epitaxial heterointerface of antiperovskite and perovskite. We are seeking multiple applications of the newly designed heterostructure thin film.