Technical. This project addresses hydrogen defects in semiconductors, ferroelectrics, and insula-tors primarily through vibrational lifetime measurements. A major goal is to directly measure the vibrational energy transfer between two local vibrational modes of the same defect utilizing a two-color pump-probe transient bleaching approach. The project aims for a comprehensive study of vibrational lifetimes, microscopic dynamics and energy absorption in model crystalline semi-conductors and metal oxides. The focus is on wide band-gap and proton conducting oxides, in-cluding ZnO, MgO, SnO2, TiO2, BaTiO3, SrTiO3, and KTaO3. The ability to directly probe these pathways and rates allows tests of theory and scaling laws at new levels of precision. Dy-namical studies will provide new insight into the coupling of the ionic surroundings to the O-H vibration and the migration of protons within the oxide crystal lattice. The high-power tunable infrared radiation from the Free-Electron Laser at Jefferson Laboratory will be utilized to inves-tigate photo-induced H diffusion in proton conducting oxides. The proposed research is expected to lead to new fundamental understanding of basic energy transfer processes in electronic and photonic materials. Non-Technical. The project addresses fundamental research issues in a topical area of electronic and photonic materials science having technological relevance. The project integrates research and education providing graduate and undergraduate students with laboratory experience and training while conducting forefront research in an interdisciplinary field including modern optics, materials science and computational modeling.
Within the NSF# DMR-0855081 award work, we have conducted measurements of the vibrational lifetime of the O-H stretch mode in various metal oxide materials. We found a giant enhancement of hydrogen transport in rutile TiO2 at low temperatures. Measurements of the O-H and O-D vibrational lifetimes show that the room-temperature hydrogen diffusion rate in rutile TiO2 can be enhanced by nine orders of magnitude when stimulated by resonant infrared light. We find that the local oscillatory motion of the proton quickly couples to a wag-mode-assisted classical transfer process along the c-channel with a jump rate of greater than 1 THz and a barrier height of 0.2 eV. Such an increase in proton transport rate at moderate temperatures is significant for renewable energy applications ranging from fuel cells to hydrogen production. Proton (H) conduction in solids is a fundamental process that has attracted considerable attention based on important developments and applications in hydrogen energy research. Particularly in the case of solid oxides, this phenomenon is usually observed at high temperatures in the range of 700 – 1000 °C. The thermal energy is required to break the O-H bond so that the proton can move between oxygen (O) atoms. This requirement limits the practical application of devices. For example, in solid oxide fuel cells high temperatures cause slow startup times, reduce operational lifetimes due to thermal stress, and require the use of expensive catalytic electrodes. Therefore, it is of great interest to develop mechanisms that can promote a high conductivity without the drawbacks associated with high-temperature operation. The NSF# DMR-0855081 award work has resulted in a US patent (no. US 20100119889), entitled "Solid Oxide Proton Conductor System and Method of Operating Same for Enhanced Proton Transport." Moreover, Phenom Technology Inc. was established in 2010 by the PI and the graduate students working on this project to develop and commercialize the novel photo-enhanced hydrogen transport technology for proton conducting solid oxide applications.
