Magnetic Resonance of Metal Hydrides and Transfer of Laser-Generated Polarization

Washington University, Saint Louis MO

Investigators

Abstract

The position and atomic motions of H and D atoms in the trihydrides (and trideuterides) YH3, LuH3, and LaH3 are important to understanding the electronically insulating nature of these 'switchable mirror' materials. Deuterium NMR will be used to identify the sites occupied and will be particularly important in LaDx, where the deuterium/metal ratio can be varied continuously from x=2 (metallic) to x=3 (insulating). NMR will also be used to look for cell-to-cell inequivalences in the lanthanum species and to study the phase transition at 240K in ZrBe2D1.5. High power diode laser-based optical pumping techniques will be used to produce 129Xe in liter quantities with nuclear spin polarization up to 40%. This polarization is up to 100,000 times that of Xe gas in thermal equilibrium at typical fields and temperatures. The goal is to devise methods for transferring the spin polarization from 129Xe to spins of analytical interest, such as hydrogen, 13C, 15N, etc. Such transfer methods could revolutionize the sensitivity of analytical NMR, allowing samples of 1 microgram or less to be examined. %%% Many metals absorb hydrogen readily, making them useful for applications such as hydrogen fuel storage devices and batteries. In this project the various aspects of the behavior of such metal hydrogen systems, 'metal hydrides,' will be investigated by means of the nuclear magnetic resonance (NMR) technique. An example is the 'switchable mirror' behavior of the metal trihydrides involving the metal yttrium, lutetium, or lanthanum. The fundamentals of this phenomenon need to be better understood in order to utilize this behavior in practical devices. Other properties of the metal hydrides will also be investigated. In recent years it has become possible to use laser light to orient the nuclear spins of certain isotopes of xenon and helium gases, which thereby have become 'nuclear spin polarized.' The resulting enhancement of NMR signal strength by factors up to 100,000 has already found applications in medical diagnostics. Further applications are envisioned by transferring the spin polarization to the nuclear spins of atoms in molecules of biological and/or chemical interest, such as carbon, hydrogen, or nitrogen. This research is directed to explore the possibilities of such polarization transfer. Graduate and undergraduate students will participate in this research. They will thereby acquire knowledge and skills that will prepare them for employment in forefront areas of condensed matter physics and materials science. ***