Корреляционный параметр Хейвена для диффузии фтора в супериониках La-=SUB=-1-y-=/SUB=-Sr-=SUB=-y-=/SUB=-F-=SUB=-3-y-=/SUB=-

The processes of electric charge transfer (conductivity) and mass transfer (diffusion) in La_1 ‒ _ y Sr_ y F_3 – _ y superionic conductors are determined by mobile fluorine ions. The fluorine random-diffusion coefficients D _σ have been calculated from experimental data on the ionic conductivity σ_ dc for La_1 ‒ _ y Sr_ y F_3 – _ y single crystals at the SrF_2 dopant contents of 1, 3, 5, 7.5, 10, and 15 mol %. A maximum in the region of 3–5 mol % SrF_2 is observed in the dependence D _σ( y ). The value of the Haven correlation parameter H _ r = D _NMR/ D _σ ( D _NMR is the fluorine diffusion coefficient measured by NMR on ^19F nuclei) is determined; it characterizes the ion transport mechanism in La_1 – _ y Sr_ y F_3 – _ y crystals. The H _ r values are 0.75 ± 0.15, 0.45 ± 0.15, and 0.65 ± 0.15 at 400–800 K for 1, 3, and 15–16 mol % SrF_2, respectively. Superionic conductor La_0.97Sr_0.03F_2.97 with maximum σ_ dc and D _σ values has a minimum Haven parameter. The obtained H _ r values indicate that fluorine diffusion in superionic conductors La_1 – _ y Sr_ y F_3 – _ y goes not according to the vacancy mechanism involving single vacancies but by cooperative motion of F^– conduction ions.