Nuclear magnetic resonance study of the metal-nonmetal transition in lanthanum hydrides

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6901858

Chang, C T

Proton spin-lattice relaxation time (T{sub 1}) measurements have been used to investigate the metal-nonmetal (MNM) transition in the lanthanum hydride system, LaH{sub x} (2 {le} {times} {le} 3). The temperature and composition dependence of the MNM transition in this system affects the proton T{sub 1} through the electronic density-of-states at the Fermi level, N(E{sub f}). In the pure samples, T{sub 1} depends directly on N(E{sub f}) at low temperatures through the Korringa relation, (T{sub 1e}T){sup {minus}1/2} {alpha} N(E{sub f}), where T{sub 1e} is the conduction electron contribution to T{sub 1}. These measurements over the temperature range 77 {le} T {le} 200 K show that N(E{sub F}) follows free-electron behavior, N(E{sub F}) {alpha} (3 {minus} x){sup 1/3}, up to x = 2.8. In the Gd-doped samples, the Gd{sup 3+} ion moment contributes an additional relaxation rate, R{sub 1p} = T{sub 1p}{sup {minus}1}. At low temperatures (7 {le} T {le} 150 K), R{sub 1p} reflects the temperature dependence of the spectral density function of the Gd{sup 3+} ion spin fluctuations, characterized by the ion spin-lattice relaxation time {tau}{sub i}. At high temperatures (T {ge} 250 K) R{sub 1p} reflects fast atomic diffusion of proton magnetization to the Gd{sup 3+} ions, and R{sub 1p} {alpha} {tau}{sub i}. These results are summarized as follows: (a) LaH{sub x} is metallic at all temperatures at all x-values up to 2.8 < {times} < 2.9, (b) LaH{sub x} is at least weakly metallic at all x-values at low temperatures (T {ge} 150 K), and (c) for x {le} 2.87 LaH{sub x} is nonmetallic at high temperatures (T {ge} 250 K).

• Research Organization: Iowa State Univ. of Science and Technology, Ames, IA (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 6901858
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201 -- Chemical &amp; Physicochemical Properties
400700* -- Radiochemistry &amp; Nuclear Chemistry
640302 -- Atomic
Molecular &amp; Chemical Physics-- Atomic &amp; Molecular Properties &amp; Theory
74 ATOMIC AND MOLECULAR PHYSICS
CHARGED PARTICLES
DATA
DATA ANALYSIS
ENERGY LEVELS
EXPERIMENTAL DATA
FERMI LEVEL
GADOLINIUM IONS
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
IONS
LANTHANUM COMPOUNDS
LANTHANUM HYDRIDES
MAGNETIC RESONANCE
MEASURING INSTRUMENTS
MEASURING METHODS
NUCLEAR MAGNETIC RESONANCE
NUMERICAL DATA
RARE EARTH COMPOUNDS
RESONANCE
TEMPERATURE EFFECTS