Synthesis, properties, and ionic conductivity of ceramic solid electrolyte-multicomponent garnet (Y, Ln)3Fe5O12 (Ln = Gd, Er, Eu, Dy)

Polycrystalline multicomponent garnets (Y0.2Gd0.2Er0.2Eu0.2Dy0.2)3Fe5O12 were obtained by glycine-nitrate pyrolysis and coprecipitation (termed (Y,Ln)IG_pyr and (Y,Ln)IG_cop, respectively). They were analyzed by XRD, SEM, microprobe analysis, diffusion reflectance, Raman, and impedance spectroscopy. Properties of multicomponent garnets were compared with those of single-component garnets Me3Fe5O12 (Me = Y, Eu, Gd, Dy, Er) obtained by glycine-nitrate pyrolysis. Structural analysis confirmed the predominant content of the garnet phase; the Rietveld method for (Y,Ln)IG_pyr garnet revealed six different types of Fe octahedra. Elemental mapping of garnets demonstrated that Y, Eu, Er, Gd, Dy, Fe distribution in (Y,Ln)IG_pyr was more uniform than in (Y,Ln)IG_cop. The optical spectra revealed charge transfer bands O2− → Fe3+ and d-d transitions of VIFe3+ and IVFe3+ions; the band gaps were 2.45 eV and 2.42 eV for YIG and (Y,Ln)IG_pyr, respectively. Raman spectra of garnets were analyzed using a statistical approach based on the autocorrelation function and the associated parameter Δcorr; sufficient distortion of Y(Ln)O8 polyhedra has been noted in multicomponent garnet. The equivalent circuit method was used to process the impedance spectra. The electrical conductivity of single-component garnets was lower than that of multicomponent ones. The activation energy of garnet (Y,Ln)IG_pyr conductivity E_a in the temperature range 200 ÷ 625 and 625 ÷ 900 °C was 0.66 eV and 0.98 eV, respectively, which was lower than that of single-component garnets. The values of dielectric constants for (Y,Ln)IG_pyr and (Y,Ln)IG_cop (ꜫ' = 364.3 and 252.9 at 300 °C at 300 kHz) were higher than those for YIG, GdIG, ErIG, EuIG, DyIG garnets (91.5, 42.4, 232.5, 21.1, 36.2, respectively).