resumo
The substitution of scandium for iron in the Ruddlesden-Popper Sr3Fe2-xScxO7-delta (x = 0-0.3) system increases tetragonal unit-cell volume and oxygen nonstoichiometry and decreases partial p- and n-type electronic conductivities studied in the oxygen partial pressure range from 1 x 10(-20) to 0.7 atm at 973-1223 K. The solubility of Sc3+ corresponds to approximately x approximate to 0.35. The relatively low, temperature-activated hole mobility indicates a small-polaron mechanism of the electronic transport, as for undoped Sr3Fe2O7-delta. The atomistic computer simulations showed that major contribution to the ionic conductivity is provided by the oxygen sites surrounded by iron cations in the perovskite-type layers of Sr-3(Fe,Sc)(2)O7-delta structure, whereas stable ScO6 octahedra are essentially excluded from the oxygen diffusion processes. Minimum migration energy, 0.9-1.4 eV, was found for nonlinear pathways formed by the apical O1 sites linking iron-oxygen polyhedra along the c-axis and equatorial O3 positions in the perovskite-type planes. The direct O3 -> O3 jumps are characterized with higher energetic barrier, 1.5-2.2 eV. Because of the increasing concentration of vacant O3 sites induced by scandium doping, the apparent activation energy for oxygen-ionic transport decreases from about 2 eV, as observed for undoped strontium ferrite at 1123-1223 K, down to 0.95-1.15 eV for Sr3Fe2-xScxO7-delta (x = 0.2-0.3). As a result, the partial ionic conductivity of Sr3Fe1.7Sc0.3O7-delta at temperatures below 1000 K becomes higher than that in Sr3Fe2O7-delta.
palavras-chave
MIXED CONDUCTIVITY; HIGH-TEMPERATURE; PEROVSKITES; TRANSPORT; SR3FE2O6+DELTA; SR3FE2O7-DELTA; PERMEATION; STABILITY; ELECTRODE; PHASE
categoria
Chemistry; Materials Science
autores
Markov, AA; Patrakeev, MV; Kharton, VV; Pivak, YV; Leonidov, IA; Kozhevnikov, VL
nossos autores
Vladislav Kharton
Investigador Principal CovidadoGrupos