Lithium self-diffusion in some heavy metal fluoride glasses

Li self-diffusion has been studied below T _g in a series of ZrF ₄–BaF ₂–LaF ₃–LiF glasses with LiF contents of 10, 20, and 30 mol%, respectively. The D Li ∗ values range between about 10 ⁻¹² and 10 ⁻¹⁵ cm ²/s and increase with increasing LiF content from 10 to 20% by two orders of magnitude. The stable isotopes ⁶Li (enriched) and ⁷ Li and an SNMS depth profiling were used. For the precision of the diffusion data an anhydrous vacuum deposition of the ⁶Li tracer on the highly reactive glass surfaces was essential. In the glass with 30 mol% LiF no Li mobility could be determined yet with the present diffusion method. The Li diffusion is discussed and it is tried to understand why it displays a differing behaviour compared to that of the Na diffusion in respective NaF-containing glasses.