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Calculation of Defect Formation Energy from the Thermal Expansion Data for Lead Fluoride

Published online by Cambridge University Press:  16 February 2011

Brenda J. Schuler ,
T. S. Aurora ,
D. O. Pederson  and
S. M. Day
Brenda J. Schuler
Affiliation:
Philadelphia College of Pharmacy and Science, Philadelphia, PA 19104
T. S. Aurora
Affiliation:
Philadelphia College of Pharmacy and Science, Philadelphia, PA 19104
D. O. Pederson
Affiliation:
University of Arkansas, Fayetteville, AR 72701
S. M. Day
Affiliation:
Miami University, Oxford, OH 45056
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Abstract

Lead fluoride is a superionic conductor with the fluorite structure. Results of the measurement of linear thermal expansion of lead fluoride (reported earlier in literature) showed a large increase in the thermal expansion coefficient near 700 K where the ionic conductivity has been shown to exhibit a sharp increase. It is believed that thermally-generated defects in a crystal lattice affect the thermal expansion coefficient. This idea was applied in the present analysis to calculate the defect formation energy (Ef) by using the literature values of the coefficient of thermal expansion. It was assumed that the thermal expansion in excess of that produced due to the lattice anharmonicity (δ∝) is proportional to the concentration of defects (n). With this assumption, one may write: δ∝ = c nº exp(-Ef/kT), where c is a constant. For lead fluoride, a plot of ln(δ∝) versus (l/T) yielded Ef = 0.56 eV which is lower than the literature values. The assumptions in this analysis and the discrepancy in the result are discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 369: Symposium U – Solid State Ionics IV , 1994 , 325
Copyright
Copyright © Materials Research Society 1995

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