SYNTHESIS, CONDUCTIVITY AND OXYGEN DIFFUSIVITY OF SR2FE3OX

Sr2Fe3Ox samples were synthesized by solid-state reaction at 1200 degr ees C in atmospheres with various oxygen partial pressures. X-ray and neutron powder diffraction experiments were conducted to determine the crystal structure. Electrical conductivity was measured by the four-p robe method at elevated temperatures in atmospheres with various oxyge n partial pressures. The oxygen chemical diffusion coefficient was det ermined by the conductivity relaxation method. Neutron powder diffract ion shotvbed that the Sr2Fe3Ox material has a layered structure with a n orthorhombic unit cell with lattice parameters a = 11.122 Angstrom, b = 18.98 Angstrom, c = 5.585 Angstrom, and V = 1178.97 Angstrom(3). T he total conductivity of Sr2Fe3Ox increases with increasing temperatur e and oxygen partial pressure; at 800 degrees C in air, the conductivi ty is approximate to 0.5 Ohm(-1) cm(-1). Oxygen chemical diffusion coe fficient increases with increasing temperature. The coefficient at 900 degrees C approximate to 1.2 X 10(-5) cm(2) s(-1), is more than one o rder of magnitude higher than that of the mixed-conducting Sr2Fe2CoOx material. The activation energy for oxygen diffusion in Sr2Fe3Ox, deri ved from the oxygen chemical diffusion coefficient, is approximate to 0.9 eV in air. (C) 1998 Elsevier Science B.V. All rights reserved.