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THERMOTRANSPORT OF 85Sr AND 54Mn IN
POTASSIUM CHLORIDE SINGLE CRYSTALS
S. Rushbrook Williams, A. Allnatt
To cite this version:
JOURNAL D E PHYSIQUE Colloque C7, supplement au n° 12, Tome 37, Decembre 1976, page C7-371
THERMOTRANSPORT OF
85Sr AND
54Mn
IN POTASSIUM CHLORIDE SINGLE CRYSTALS
S. J. C. RUSHBROOK WILLIAMS (*) and A. R. ALLNATT (*)Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada
Résumé. — On a mesuré le thermotransport de "Sr et 54Mn dans des monocristaux de KCI dans le domaine 950-1 025 K au moyen de l'effet Soret. La chaleur de transport de l'impurité est — 3,18 ± 0,03 (1 ± 0,25) eV pour Sr en KCI pur et en KCI dopé par Sr, et il est — 5,45 ± 0,29 (1 ± 0,27) eV pour Mn en KCI pur et en KCI dopé par Mn. Il n'y a aucune différence signincante entre les cristaux purs et dopés. On a discuté les limites expérimentales et théoriques des mesures pour étudier les chaleurs de transport et l'on a comparé les résultats avec les mesures antérieures dans les cristaux ioniques.
Abstract. — The thermotransport of 85Sr and 54Mn tracers in single crystals of KCI was mea-sured in the temperature range 950-1 025 K, by means of Soret effect measurements. The mean value of the impurity heat of transport was—3.18 ± 0.03(1 ± 0.25) eV for Sr in pure or Sr-doped crystal, and was — 5.45 ± 0.29 (1 ± 0.27) eV for Mn in pure or Mn-doped crystals. There was no significant difference between values from pure and doped crystals. A discussion of the experimental and theoretical limitations of such measurements as a source of information about the heats of transport for individual jumps was given, and a comparison made with earlier thermotransport measurements in simple ionic solids.
A full account of this work is being submitted for publication elsewhere. The main points in the oral presentation which are not included in the Abstract were as follows.
The present results and earlier measurements [1] show that the alkali halides with divalent impurity tracers give systems differing widely in their suitability for Soret effect studies. KCI is peculiarly unsuitable decause of its plasticity and rapid evaporation. It was found that carefully purified crystals were essen-tial.
The kinetic analysis of thermotransport in alloys [2] using Lidiard's diffusion model [3] was extended to NaCl crystals. The heats of transport of the impurity-vacancy complex in pure crystals, Q*, and in doped crystals, Q*', were expressed in terms of the heats of transport, q*, for the five kinds of cation jump and one kind of anion jump recognized in the model. It was found that only if the dissociative jumps of the complex could be neglected did one obtain the result (*) Associated with the Centre for Interdisciplinary Studies in Chemical Physics, University of Western Ontario.
2 * = 2 * ' used earlier [1], and could one furthermore obtain useful information about the q* from Soret measurements.
The equality Q* — Q*' was confirmed experimen-tally. The values of — 2k found for Sr and Mn in KCI were much larger than those for the tight binding system Sr in NaCl [1]. It does not seem possible to determine from Soret measurements alone whether this is due to contributions arising from deviations from tight binding in the KCI systems or whether the tight binding contributions differ substantially in NaCl and KCI. In each system — Q^ is much larger than that expected by assuming each q* is equal to the corresponding enthalpy of activation and that tight binding holds. Available data on jump frequencies in KCI suggest that tight binding is not valid for Mn, but might be adequate for Sr.
Acknowledgment. — Support through an Ope-rating Grant of the National Research Council of Canada is acknowledged.
References
[1] ALLNATT, A. R. and CHAD WICK, A. V., Trans. Faraday Soc. 63 (1967) 1929.
[2] HOWARD, R. E. and MANNING, J. R„ / . Chem. Phys. 36
(1962) 910.
[3] LIDIARD, A. B., Phil. Mag. 46 (1955) 1218.
C7-372 S. J. C. RUSHBROOK WILLIAMS AND A. R. ALLNATT
DISCUSSION
P. W. M. JACOBS.
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Both the method reported at rity might be so much larger than the activation energy this conference by Rahman and Blackburn and earlier for isothermal diffusion ?thermoelectric power measurements by Jacobs and
