Correlation between crystal and transport properties in LnBa0.5Sr0.5Co1.5Fe0.5O5 + δ (Ln - selected lanthanides, Y)

Selected LnBa0.5Sr0.5Co1.5Fe0.5O5 + δ (Ln - Pr, Nd, Sm, Gd and Y) oxides were studied in terms of their phase composition, formation of cation-ordered crystal structure, oxygen nonstoichiometry and transport properties. Despite partial substitution of bigger Ba2 + by smaller Sr2 + cations, A-site (Ln-Ba,Sr) cation ordering in LnBa0.5Sr0.5Co1.5Fe0.5O5 + δ is preserved, but only for smaller Ln cations (Y3 +, Gd3 +). In the case of SmBa0.5Sr0.5Co1.5Fe0.5O5 + δ, the synthesis procedure yielded material partially ordered, while for Pr3 + and Nd3 + cations XRD measurements indicated formation of cation-disordered samples. Oxygen content in the disordered materials is close to stoichiometric one (δ ≈ 1) at room temperature, while for cation-ordered samples δ < 1. Thermogravimetric measurements indicated that above 250 °C a decrease of mass occurs for all of the studied materials. Except for Y-containing sample, larger mass loss at 800 °C occurs for materials with heavier Ln element. The ordered materials show higher activation energy of the electrical conductivity in 25–300 °C temperature range, as well as different temperature dependence of Seebeck coefficient, comparing to the disordered ones. The highest electrical conductivity was measured for PrBa0.5Sr0.5Co1.5Fe0.5O5 + δ. For this compound the ionic conductivity at 800 °C was determined to be of the order of 0.03 S cm− 1.