The dynamic properties of Li cations in the 0.3Li2O–0.7B2O3 glass were investigated by molecular dynamics simulations at 1250K by means of the van-Hove space-time correlation functions. Li cations could be distinguished into Lib and Linb types, if they reside predominantly in sites formed by bridging O atoms (b-type) or sites involving both bridging and non-bridging O atoms (nb-type), respectively, with Linb cations being more mobile than the Lib ones. The self-van-Hove correlation functions had shown that at times shorter than 15ps both types of Li cations were characterized by a non-Gaussian behavior, implying a jump-type rather than a random-walk diffusion mechanism. However, whereas for Linb cations a Gaussian distribution of jump lengths was restored at times longer than 20ps, this was not the case for Lib cations. Examination of the distinct-van-Hove correlation functions had shown that Linb ions migrate by hopping into nb-type sites, whereas hopping into a b-type site was a process of negligible probability. On the contrary, the hopping process of Lib cations involved jumps into both nb- and b-type sites, as well as into interstitial sites.

Cation Dynamics in Lithium Borate Glasses. C.P.E.Varsamis, A.Vegiri, E.I.Kamitsos: Journal of Non-Crystalline Solids, 2002, 307-310, 956-62