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Non-Random Mixing and Fast ion Decoupling in Lithium Chloroborate Superionic Glasses: An Ion Dynamics Computer Simulation Study

Published online by Cambridge University Press:  21 February 2011

R. Syed ,
J. Kieffer  and
C.A. Angell
R. Syed
Affiliation:
Department of ChemistryPurdue UniversityWest Lafayette, IN 47907 On summer leave fron Physics Department, Norwich University, Norlhfield, VT 05663
J. Kieffer
Affiliation:
Department of ChemistryPurdue UniversityWest Lafayette, IN 47907
C.A. Angell
Affiliation:
Department of ChemistryPurdue UniversityWest Lafayette, IN 47907
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Abstract

Li+ ions are highly mobile in LiCl-Li2O·2B23 glasses to the extent that the decou-pling of conductive modes of motion from the viscous modes, assessed at the glass transition temperature Tg by a relaxation time ratio, is one of the greatest known. The interpretation of the structure of this glass system and its relation to conductivity decoupling is not very advanced at this time but there seems to be a distinction drawn between the chloroborate structure and the structure of the corresponding AgCl-Ag borate and AgI-borate glasses. The latter have frequently been discussed in terms of α-AgI percolating clusters although the available thermodynamic evidence indicates chemical ordering (negative deviations from ideal mixing) as opposed to any sort of clustering (positive deviations from ideal mixing). The LiCl-Li2O-B2O3 system is interesting to us because simple transferable effective pair potentials are available for all species in the system and ion dynamics computer simulations should be capable of giving useful insights into the structure, energetics, and dynamics of the system. We present diffusivity data as a function of temperature for several compositions in the LiClLi2O·2B2O3 system and observe that the Li+ mobility remains high below the simulated, glass transition. Surprisingly, the Cl− anion mobility also remains high, raising a question about anion transport numbers in these glasses. Computed conductivities agree with laboratory data in the liquid state but exceed laboratory data in the glassy state in the direction expected from the high fictive temperature of simulated glass. Deviations from additivity in mixing energy in this system show a weak tendency to clustering of LiCl in the structure which suggests a need for laboratory mixing enthalpy studies.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 135: Symposium M – Solid State Ionics I , 1988 , 63
Copyright
Copyright © Materials Research Society 1989

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