The O permeability of dense garnet-type Gd3–xAxFe5O12±δ (A = Ca, Pr; x = 0 to 0.8) and Y3–x–yCaxNdyFe5–zNizO12–δ (x = 0 to 0.5; y = 0 to 0.25; z = 0 to 1) membranes at 1173 to 1273K was studied. The ion transference numbers, as calculated from results on O permeation and total conductivity, varied from 10–5 to 5 x 10–3, and increased with temperature. The ionic conduction in ferrite garnets, which was governed mainly by the O vacancy concentration, increased with acceptor dopant additions. The activation energies for O-ionic and electronic transport in air were 176 to 224 and 20 to 81kJ/mol, respectively. The ceramic microstructure of the garnet-based materials had no essential effect upon the ionic conductivity; which was low when compared with that of perovskite-related ferrites. A low mobility of O ions, which was probably limited by ion transfer along the edges of Fe-O tetrahedra in the garnet lattice, was thought to be likely to result from a crooked diffusion pathway. Decreasing the A-site cation radius led to a higher ionic conductivity of the garnet phase.

Ionic Transport in Gd3Fe5O12- and Y3Fe5O12-Based Garnets. V.V.Kharton, A.L.Shaula, E.N.Naumovich, N.P.Vyshatko, I.P.Marozau, A.P.Viskup, F.M.B.Marques: Journal of the Electrochemical Society, 2003, 150[7], J33-42