Synthesis, crystal chemistry, and electrical, oxygen permeation, and magnetic properties of LaSr3GaFe2 − xCoxO10 − δ (0 ≤ x ≤ 2 and 0 ≤ δ ≤ 2)

Abstract

The crystal chemistry and electrical, oxygen permeation, and magnetic properties of the n = 3 member of the Ruddlesden–Popper (R–P) series of phases LaSr₃GaFe_{2 − x}Co_xO_{10 − δ}, with 0 ≤ x ≤ 2 and 0 ≤ δ ≤ 2, have been investigated. While the orthorhombic cell parameters a and b and the unit cell volume decrease, the c parameter increases with increasing Co content. Conductivity measurements show that the samples exhibit a thermally activated process, with 0.17 ≤E_a ≤ 0.35 eV. The oxygen permeation flux values (jO₂ ≈ 1 × 10⁻⁹ mol s⁻¹ cm⁻²) at 900 °C across 1.5 mm thick LaSr₃GaFe_{2 − x}Co_xO_{10 − δ} membranes are two orders of magnitude lower than those observed previously with other n = 2 and 3 R–P phases (tetragonal) due to the orthorhombic distortion and negligible oxygen vacancy concentration gradient across the membrane. The reduction of the LaSr₃GaFe_{2 − x}Co_xO_{10 − δ} phases in a mixture of 90% Ar and 10% H₂ leads to the formation of LaSr₃GaFe_{2 − x}Co_xO_{9 − x/2} phases containing Co²⁺ and with orthorhombic symmetry. SQUID magnetometer data indicates antiferromagnetic interactions and the presence of high spin Co³⁺ ions in the LaSr₃GaFe_{2 − x}Co_xO_{9 − x/2} phases.