University of Illinois Urbana-Champaign

Study of tunneling impurities in alkali halides at low temperatures

Dobbs, James Norris

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https://hdl.handle.net/2142/25282

Description

Title
Study of tunneling impurities in alkali halides at low temperatures
Author(s)
Dobbs, James Norris
Issue Date
1985
Doctoral Committee Chair(s)
Anderson, A.C.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • tunneling impurities
  • alkali halides
  • specific heat
  • thermal expansion
  • Schottky anomaly
Language
en
Abstract
The impurity tunneling systems of Li+ in KCl and CN-in KBr have been studied by means of specific heat (C) and thermal expansion (a) measurements obtained at temperatures T between 0.09 K and 10 K. For the Li+ defects, a peak occurs in the thermal expansion near 1 K which is qualitatively similar to the Schottky anomaly observed in the specific heat. For T > 0.6 K, the GrUneisen parameter, r, 3a/C, is isotropic and tt equal to +150±15 independent of temperature and lithium isotope. At lower temperatures, r becomes temperature dependent and anisotropic with respect to crystal orientation, probably because of interactions between Li+ sites. All measurements were for Li+ concentrations < 200 ppm. The KBr:CN system has been studied for CN-concentrations ranging from 0.034% to 50%. At the lowest concentration, the thermal expansion consists of a positive peak near 1 K (r ~ +50) and a negative peak near 0.2 K (r ~ -100). As the CN-concentration is increased, the thermal expansion becomes smaller in magnitude and in temperature dependence as the orientational glass phase develops. At 50% concentration, the thermal expansion (with r ~ +1) is similar to that of many amorphous solids.
Type of Resource
text
Permalink
http://hdl.handle.net/2142/25282
Copyright and License Information
Copyright 1985 James Norris Dobbs

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