Forschungsbericht 1999-2000 | |
Institut für Materialphysik (ehemals Institut für Metallforschung) Wilhelm-Klemm-Str. 10 48149 Münster Tel. (0251) 83-3 35 71 Fax: (0251) 83-3 83 46 e-mail: mehrer@nwz.uni-muenster.de WWW: http://www.uni-muenster.de/Physik/MF Geschäftsführender Direktor: Prof. Dr. H. Mehrer | |
Forschungsschwerpunkte 1999 - 2000
Fachbereich 11 - Physik Institut für Materialphysik Ionic Motion in Materials with Disordered Structures | ||||
Diffusion and ionic conductivity in borate glasses
Diffusion of 22Na was studied in x
Na2O · (1-x) B2O3 glasses with
x = 0.2 and x = 0.3 using the radiotracer method. A slight decrease of
the diffusion coefficients with increasing diffusion time was observed and is attributed to a
structural relaxation of the glass network. The temperature dependence of diffusion was
measured below and also in a small temperature range above the glass transition temperature
(TG). Below TG the diffusion coefficients obey Arrhenius relations.
Diffusion in the glass with higher Na content is considerably faster. The results are compared
with dc conductivity data.
The pressure dependence of 22Na diffusion in 0.3 Na2O ·
0.7 B2O3 yields an activation volume of 0.52 molar volumes.
This relatively high value indicates a significant relaxation of the glass network associated with
a Na jump.
In sodium-rubidium borate glasses with a total alkali content of 30 mol percent and
Na/(Na+Rb) ratios between 0.4 and 1.0 diffusion of 22Na and 86Rb
was investigated at 673 K. Diffusion of alkali ions in mixed-alkali borate glasses shows
a concentration dependence which is different from published mixed-alkali effects for
diffusion in silicate glasses. Sodium diffusion is always faster than rubidium diffusion. Na
diffusion shows a minimum and Rb diffusion a maximum for a relative concentration of about
60 % sodium. The ionic conductivity deduced from the diffusivities displays a minimum
as a function of the relative composition of sodium like in other mixed-alkali oxide glasses.
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Hans-Joachim Peter