Phonon scattering from substitutional impurities and lattice defects in silver chloride
Chau, Cheuk-Kin
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https://hdl.handle.net/2142/25755
Description
Title
Phonon scattering from substitutional impurities and lattice defects in silver chloride
Author(s)
Chau, Cheuk-Kin
Issue Date
1968
Doctoral Committee Chair(s)
Klein, Miles V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
phonon scattering
substitutional impurities
lattice defects
silver chloride
thermal conductivities
infrared absorption
Language
en
Abstract
The purpose of this investigation was to study phonon scattering
by substitutional impurities and lattice defects in silver chloride
crystals by means of the thermal conductivity technique. In addition,
far infrared absorption measurements were made on some of the doped
crystals.
The thermal conductivity of silver chloride as a function of the
concentrations of eight impurities-- Li+, Na+, K+, Rb+, uC +, Cu + + , Br - and
I---was measured in the temperature range 1.2°K to 80 0 K. Only in the
quenched heavily doped lithium crystal was a definite therma1 conductivity
dip observed. The strong low temperature depressions in the thermal conductivity
of the peavi1y doped Li+ and Cu++ doped crystals suggest possib1e
resonance below 10 K.
The far infrared absorption of some of the doped crystals was
measured from 33 cm -1 to 105 cm -1 at 7 ° K. Impurity induced absorption
peaks were observed in all cases, except for the rubidium doped crystal
where the concentration was perhaps too low to give rise to any induced
absorption.
The thermal conductivity of pure silver chloride crystals, which
were subjected to various heat and surface treatments, was measured. The
results suggest that the phonon scattering is mainly due to dislocations
and that diffusive boundary scattering is perhaps due to the dynamical
dislocation loops beneath the surface.
The pure single crystal thermal conductivity curve was fitted by
using the Debye thermal conductivity integral. Due to the existence of
many low energy critical points, a two group velocity model was employed.
A relatively strong normal process relaxation rate suggests that anharmonicity
may be important.
More information about the phonons in the silver chloride lattice
is needed in order to perform significant analysis on the far infrared
absorption spectra.
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