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Ionic Conduction Mechanisms in CaF2 and CaF2-Al2O3 Nanocomposite Films on Al2O3 Substrates

Published online by Cambridge University Press:  21 February 2011

F. A. Modine ,
D. Lubben  and
J. B. Bates
F. A. Modine
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6030
D. Lubben
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6030
J. B. Bates
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6030
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Abstract

Thin films of pure CaF2 and nanocomposite mixtures of Al2O3 with CaF2 were sublimated on Al2O3 substrates. Interdigital electrodes allowed in situ measurements of the electrical conduction of films as a function of thickness, deposition rate, composition, time, and temperature. The electrical conductivity in pure CaF2 adjacent to an Al2O3 interface sometimes exceeded the bulk CaF2 conductivity (i.e., value at more than 50 nm distance) by as much as a factor of 6700 at 200°C. The high conductivity is characterized by an activation energy of 0.6 ± 0.1 eV, which is significantly lower than the activation energy of about 1.0 eV for conduction in the bulk. However, this high conductivity is thermally unstable and diminishes in time. A high but stable conductivity was obtained in CaF2 films containing about 10 mole percent Al2O3 as a dispersed second phase. At 200°C, a 2-phase film gave a factor of 360 enhancement over the measured bulk CaF2 conductivity and a factor of 7 improvement over the best previously reported conductivity for CaF2-Al203 composite materials. The origin of enhanced conduction in CaF2 is attributed to ion transport along dislocations. Dislocations anneal with a characteristic log of time dependence that is recognizable in the annealing behavior of the electrical conductivity. Presumably, the addition of a dispersed second phase of Al2O3 to CaF2 serves both to generate and to pin dislocations; the electrical conductance is thereby enhanced and stabilized.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 318: Symposium Ca – Interface Control of Electrical, Chemical, and Mechanical Properties , 1993 , 439
Copyright
Copyright © Materials Research Society 1994

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References

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