Characterization of perovskite-type cathode, La_0.75Sr_0.25 Mn_0.95-xCo_x Ni_0.05O_3+δ (0.1 ≤ x ≤ 0.3), for intermediate-temperature solid oxide fuel cells

Phase evolution, structure, thermal property, morphology, electrical property and reactivity of a perovskite-type cathode system, La_0.75Sr_0.25 Mn_0.95-xCo_xNi_0.05O_3+δ (0.1 ≤ x ≤ 0.3), are reported. The samples are synthesized using metal acetates by the Pechini method. A perovskite-type phase is formed after calcination at ∼700 °C and a rhombohedral symmetry of R - 3c space group is stabilized at ∼1100 °C. An increase in x decreases the unit cell volume linearly, accompanying with a linear decrease in bond lengths and tilt angle. The differential thermal analysis suggests the phase stabilization for a temperature range, 50-1100 °C. The thermo-gravimetric, thermal expansion, and electrical and ionic conductivities studies suggest presence of a Jahn-Teller transition at ∼260-290 °C. The samples with x = 0.1 mol exhibit electrical conductivity of ∼55 S cm^-1 at ∼600 °C, activation energy of ∼0.13 eV, coefficient of thermal expansion of ∼12 × 10⁶ °C^-1, crystallite size of ∼45 nm, Brunauer-Emmett-Teller (BET) surface area of 1.26 m² g^-1 and average particle size of ∼0.9 μm. A fairly high ionic conductivity, 5-9 × 10^-2 S cm^-1 makes the sample with x = 0.1 mole suitable for intermediate-temperature solid oxide fuel cell cathode applications. The experimental results are discussed with the help of the defect models proposed for La_1-xSr_xMnO_3+δ.