Study of tunneling impurities in alkali halides at low temperatures

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Dobbs, James Norris

Contributors dc:contributor

• Anderson, A.C.

• tunneling impurities
• alkali halides
• specific heat
• thermal expansion
• Schottky anomaly

Statement dc:rights

• Copyright 1985 James Norris Dobbs

Language dc:language

en

Identifier

842396

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25282