Lithium isotopes mobility

It is also interesting to compare the eigen mobilities of Li and Li with the mobilities Uq and W7 in mixtures of the lithium isotopes. For liquid LiCl (23, 42) and solid Li2S04 (5i) the difference is... 

A decrease with rising temperature has also been observed for the relative differences of the external mobilities (250°-350°C.) of the lithium isotopes in eutectic NaNOs-KNOs mixtures (2). On the other hand the relative differences of the external mobilities of the sodium isotopes Na and Na in LiNOs (305°-359°C.) and in eutectic NaNOa-KNOs mixtures (255°-374°C.) rise with rising temperature (in the latter case the increase is followed by a decrease in the range 374°-434°C.) (70). 

This indicates a cooperative motion of the lithium ions. If the concept is adopted that a lithium ion always moves as a member of a group of n lithium ions, and that the momentary mobility of an ion is the mean of the eigen mobilities of the momentary members of the group it belongs to, the mean isotopic lithium mobilities in a mixture will be... 

In theory, diffusion coefficients can be measured for any ion. In practice, however, most studies of ionic diffusion in glasses have been restricted to highly mobile ions which have a convenient radioactive isotope for use in tracer measurements. As a result, a majority of the data for ionic diffusion deals with sodium, with lesser amounts of data for potassium, rubidium, and cesium. Studies of lithium are very limited due to the lack of a radioactive isotope of lithium, while studies of divalent and other, more highly charged, ions are restrieted by the very low mobilities of these ions as compared to those of the monovalent ions. 

By using isotopic enrichment, the contributions of Li" " and Na mobility to the total conductivity have been decoupled. " Despite the difference in cation size and typical coordination environments lithium and sodium show similar activation energies of ca 0.64 eV and make similar contributions to the overall conductivity of the phase. This observation is incompatible with the simple view of a positive cation migrating through a static window and indeed it has been shown that the sulfate anions in LiNaS04 are dynamic in the P phase. There is an energy barrier to anion... 

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