Exchange dynamics of /sup 23/Na and structural incommensuration in NaMo/sub 4/O/sub 6/: Dynamic line shape for the second order central transition of quadrupolar nuclei

Journal Article · Sat Apr 01 00:00:00 EST 1989 · J. Chem. Phys.; (United States)

OSTI ID:6229558

Chu, P J; Gerstein, B C

Sodium nuclei in NaMo/sub 4/O exhibit motion as evidenced by the change in asymmetry parameter describing the central transition of /sup 23/Na with variable temperature. The nonaxially symmetric electric field gradient observed in the slow motion limit implies that the preferred occupation of the sodium nucleus is not at the center of the tetragonal oxygen cage. At room temperature the sodium jumps randomly within the cage in such a manner as to experience an axially symmetric electric field gradient on average. Dynamic NMR line shape simulations invoking second order broadening of the central transition were performed based on models of four site exchange, and all-site random exchange. Both models yield results indistinguishable from experiment, with an activation energy E/sub a/ of 1.95 k cal mol/sup -1/. An anomolous upfield shoulder in the central transition is related to the existence of a structural incommensuration. A lower transition temperature T/sub c/ = 140 K is evidenced by jump discontinuities in both the temperature dependence of T/sub 1/ and of the quadrupolar coupling constant e/sup 2/qQ. Using a plane wave approximation to describe the structural incommensuration, the appearance of, and the gradual downfield shift of the upfield shoulder can be satisfactorily fit to the data. From the temperature dependence of the quasicontinuous frequency distribution associated with the incommensurate structure, the upper transition temperature T/sub i/ is estimated to be 520 K.

• Research Organization: Institute for Physical Research and Technology, and Department of Chemistry, Iowa State University, Ames, Iowa 50011
• OSTI ID: 6229558
• Journal Information: J. Chem. Phys.; (United States), Vol. 90:7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MOLYBDENUM OXIDES
CRYSTAL-PHASE TRANSFORMATIONS
SODIUM OXIDES
COUPLING CONSTANTS
EXPERIMENTAL DATA
LINE WIDTHS
NMR SPECTRA
POWDERS
QUADRUPOLE MOMENTS
SODIUM 23
TEMPERATURE DEPENDENCE
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
CHALCOGENIDES
DATA
INFORMATION
ISOTOPES
LIGHT NUCLEI
MOLYBDENUM COMPOUNDS
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
REFRACTORY METAL COMPOUNDS
SODIUM COMPOUNDS
SODIUM ISOTOPES
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies