Internal friction study on the lithium ion diffusion of Li5La3M2O12 (MÂ =Â Ta, Nb) ionic conductors

► Two relaxation peak were observed in the Li5La3M2O12 (M = Ta, Nb). ► The peaks are associated with the jumps of lithium ions between different sites. ► Lithium ions jump not independently but in a correlated manner. ► The coupling model can not well describe the correlated jumps of lithium ions.