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https://hdl.handle.net/2142/25452
Description
Title
Lattice dynamics of Chevrel phase compounds
Author(s)
Holmgren, Donald John
Issue Date
1987
Doctoral Committee Chair(s)
Ginsberg, D.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
lattice dynamics
chevrel phase compounds
Brillouin zone-center phonons
Raman spectroscopy
Language
en
Abstract
Single crystals of the Chevrel phase compounds BaMo6Sg, Cu1.gMo6Sg,
Cu3.2Mo6Sg, PbMo6Sg, and SnMo6S8 were prepared by solidification and vapor
techniques. Because of the incongruent melting behavior of some of these compounds and
because of their high melting points, a pressurized radio-frequency furnace was designed,
built, and used for the melt growth of crystals. Crystals as large as 125 mm3 were grown.
The energies and symmetries of Brillouin zone-center phonons of these crystals were
measured by Raman spectroscopy. These energies are in good agreement with data reported
in the literature obtained by measurements of superconducting tunnel junctions. The Raman
data, extending over a larger energy range, complement the tunnel-junction data.
The Raman data show that the energies of the phonons in these compounds are
roughly independent of the particular central metal atom. Small differences in the observed
frequency of corresponding phonons in PbMo6Sg, SnMo6Sg, and Cu1.gMo6S8 may be a
factor in determining their superconducting transition temperatures. Differences in observed
frequencies of corresponding phonons in Cu 1.sMo6Ss and Cu3.2Mo6S8 are correlated with
the differences in interatomic distances, and indicate the dominance of sulfur atom motions in
these normal modes.
Numerical lattice-dynamics calculations were performed. The calculation parameters
were varied to fit the experimental data. The results of the calculations include descriptions
of the motions of the atoms in the various normal modes, dispersion curves, and phonon
density of states curves.
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