PROTON MOTION, KNIGHT SHIFTS, AND QUADRUPOLAR EFFECTS IN THE LANTHANUM- HYDROGEN SYSTEM

Journal Article · Thu Aug 01 04:00:00 EDT 1963 · Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D

DOI:https://doi.org/10.1103/PhysRev.131.1118· OSTI ID:4688379

Scheiber, D S; Cotts, R M

The nuclear magnetic resonance of both the lanthanum and hydrogen nuclei in the lanthanum-hydrogen system has been studied as a function of hydrogen concentration and temperature. The concentrations ranged from 0.4 H/La to 2.85 H/ La and temperatures -197 deg C to 400 deg C. The existence of two phases, part La metal and part LaH/sub 2.0/ for concentrations with less than 2 H/La, is confirmed. Measurements of the proton linewidth and thermal relaxation time T/ sub 1/ unambiguously demonstrate that proton self-diffusion takes piace at moderate temperatures. Activation energies and attempt frequencies for the proton self-diffusion, which are determined as a function of hydrogen concentration, decrease abruptly at approximately 2 H/La from 23 kcal/mole and 10/sup 14/ sec/sup -1/, respectiveiy, to 3 kcal/mole and 10/sup 11/ sec/sup -1/at 2.85 H/La. The proton static linewidths vary continuousiy from 7.8 g at 2 H/La to 12.4 g at 2.85 H/La and the proton T/sub 1/ has a characteristic self- diffusion induced minimum of approximately 5 to 8 msec and a maximum of approximately 100 msec where spin diffusion to paramagnetic impurities dominates. The self-diffusing protons have a pronounced effect, via a quadrupole interaction, on the La resonances. For hydrogen concentrations slightly greater than 2 H/La, a broadening and then narrowing again of the La linewidth, and a decrease with a subsequent recovery of the La Knight shift is observed as the proton self-diffusion rate increases with temperature. For concentrations greater than 2.4 H/ La, no La resonance is observed until a sufficiently high proton self-diffusion rate is attained to average out the quadrupolar effects. A detailed semiquantitative analysis incorporating the proton resonance data is made of these quadrupolar effects. At 400 deg C the La Knight shift is found to decrease from 0.23% for 2 H/La to 0.10% for 2.85 H/La while no Knight shift is observed for the proton resonance at any concentration or temperature. The thermal relaxation time of the La resonance in LaH/sub 2.0/ is found to be the result of a conduction electron hyperfine interaction with T/sub 1/T = 11.3 sec deg K when the protons are static. With proton motion the La T/sub 1/ decreases exponentially to a value somewhat greater than the La T/sub 2/ or about 100 mu sec at 400 deg C. A schematic picture of the band structure of the hydride consistent with the available data is suggested, based on an ionized hydrogen atom or proton, whose electron goes into a conduction band localized on the La ion. (auth)

• Research Organization: Cornell Univ., Ithaca, N.Y.
• NSA Number: NSA-17-031191
• OSTI ID: 4688379
• Journal Information: Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D, Journal Name: Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D Vol. Vol: 131; ISSN PHRVA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ACTIVATION
DIFFUSION
ELECTRIC CONDUCTIVITY
ELECTRONS
ENERGY
ENERGY LEVELS
FREQUENCY
HYDROGEN
HYPERFINE STRUCTURE
IMPURITIES
INTERACTIONS
IONS
KNIGHT SHIFT
LANTHANUM
LANTHANUM HYDRIDES
LIFETIME
MAGNETIC MOMENTS
MAGNETISM
MEASURED VALUES
METALS
MIXING
MOTION
NUCLEAR MAGNETIC RESONANCE
NUCLEI
PARAMAGNETISM
PHYSICS
PROTONS
QUADRUPOLE MOMENTS
QUANTITY RATIO
RESOLUTION
SELF-DIFFUSION
SPIN
TEMPERATURE
VARIATIONS