Proton Tunneling in Perovskite Oxides Gunter Lüpke, College of William and Mary, DMR 0600861

1. Proton Tunneling in Perovskite Oxides Gunter Lüpke, College of William and Mary, DMR 0600861 Proton tunneling is an important underlying transfer process in many physical systems, closely related to the energy dynamics of the proton and its local environment. Perovskite oxides, such as KTaO3, are well established proton conductors, however tunneling transport has seen little experimental investigation and has not been linked to the vibrational dynamics of the O-H bonds common to the oxides. Vibrational lifetime measurements of the O-H and O-D stretch modes in KTaO3 are a unique way to probe these microscopic dynamics and have shown direct evidence of proton tunneling. The experimental proton tunneling rate has been extracted from the O-H and O-D lifetimes and is in good agreement with a model for a phonon-assisted tunneling process. Ionic conduction in the perovskite lattice involves the hopping or tunneling of protons (red) between oxygen atoms (blue). The vibrations of the oxygen atoms (blue arrows) alters the potential barrier between oxide ions, allowing the proton to tunnel. Vibrational lifetime measurements of the O-H and O-D stretch modes in KTaO3. The results are the first in an oxide system, exhibiting extremely long lifetimes (up to 400 ps) and an unexpected “reverse” isotope effect. These findings indicate that hydrogen vibrational modes can decay via proton tunneling - a new decay mechanism! Phys Rev. Lett. 102, 075506 (2009)

2. Proton Tunneling in Perovskite Oxides Gunter Lüpke, College of William and Mary, DMR 0600861 Investigations into vibrational dynamics of protons in oxides are of utmost importance for understanding and advancing the current state of the art in a multitude of scientific disciplines. Proton transport through fuel cell electrolytes, the energetics of protein reactions and hydrogen storage devices all involve the dynamical motion of protons, which as we show in our work, can be strongly influenced by the quantum mechanical tunneling transfer of protons. Top: Fuel Cell Electrolyte Bottom: Proton double well potential energy surface and proton tunneling rate, kPT.