Hafnia under external stimuli

NON-TECHNICAL DESCRIPTION This program is inspired by opportunities to explore the different metastable phases of hafnia (HfO2) under external stimuli and to invest in the education of students at the University of Tennessee. Both initiatives merit broad support because they will advance the fundamental understanding of new states of matter in oxide dielectrics and contribute to important societal values and outcomes. A variety of different phases of hafnia will be studied to unravel mechanical and tribological properties, switching pathways, and the appearance of elusive or metastable phases driven by pressure. Structure-property relationships are also of interest. A broad range of educational, outreach, and service activities will also take place under the auspices of this National Science Foundation-funded program, especially in the areas of increasing the STEM workforce, conference and workshop organization, and service to various national laboratories. TECHNICAL DESCRIPTION The research outlined in this proposal focuses on the spectroscopic properties of hafnia and the application of pressure and electric field to drive phase transformations. The project combines synchrotron-based infrared absorption and Raman scattering with diamond anvil cell techniques, lattice dynamics calculations, symmetry arguments, and an analysis of energy landscapes with selected resonant x-ray, mechanical, and tribological properties work to (i) identify high pressure routes to new states of matter, (ii) reveal mode Gruneisen parameters along with mechanical and tribological properties, (iii) test how to create stabilizer-free single crystals of HfO2 using high pressure techniques rather than high temperature growth, (iv) search for evidence of soft mode instabilities, and (v) resolve controversy regarding the ferroelectric switching pathway in the polar orthorhombic material. The project is also interested in the structure-property relationships that can be unraveled in this system. What brings these efforts together is interest in light-matter interactions under extreme conditions and the spectroscopic techniques that are investigated. Findings from this program are advancing theoretical development and semiconductor chip applications. This program also supports the interdisciplinary education of young researchers for future employment in academics, government laboratories, and industry in the area of advanced materials. 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.