RII Track--4: Controlling Point-Defect Energetics in Complex Oxides Via Interfacial Strain

What silicon was to the 20th century, quantum materials are to the 21st. A million times faster computers than today's most powerful supercomputers, or, electricity transported across the national grid at no loss, is the sort of future that will be realized by the power of quantum materials. Realizing this vision requires developing new materials and understanding key materials features that give rise to such incredible properties. Interfacial oxide materials, i.e., those formed by joining of two different oxide materials, are one of such promising materials. An example of an interfacial oxide material is an interface between LaNiO3 and SrTiO3. Because these two materials have different distances between their atoms, when joined to form an interface, their atomic bonds are strained that can lead to creation of defects, i.e., loss of specific oxygen atoms. Creation of these defects has been proposed to be a key underlying reason of such exciting properties. In this project, we focus on understanding the critical correlation between strain and oxygen defects such that the defects could be controlled, at will. This work will advance Wyoming's vision of computational sciences, develop basic understanding of designing quantum materials, and contribute to "The Quantum Leap: Leading the Next Quantum Revolution" which is one of the next ten big NSF ideas. The interface structure formed by joining two different complex oxides (chemical formula ABO3) contains an interfacial strain which leads to formation of oxygen vacancies at the interface. These vacancies are considered to be one of key reasons inducing many novel electronic properties. The overarching goal of the proposal is to develop a fundamental understanding of the correlation between interfacial strain and oxygen vacancies in LaNiO3 grown on SrTiO3. This correlation will allow control over the stability (i.e., location and concentration) of vacancies via strain, at will. In-situ X-ray Photon Correlation Spectroscopy (XPCS) experiments at Advanced Photon Source (APS) in Argonne National Laboratory and density functional theory calculations will be used to elucidate the thermodynamics and kinetics of phase transitions in LaNiOx phases, which appears to be induced via the ordering and disordering of the oxygen vacancies. This understanding will advance the science of gaining control over the metal-insulator transition temperature in LaNiO3. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.