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

Abstract

Selected LnBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + 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 Ba 2 + by smaller Sr 2 + cations, A-site (Ln-Ba,Sr) cation ordering in LnBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + δ is preserved, but only for smaller Ln cations (Y 3 + , Gd 3 + ). In the case of SmBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + δ , the synthesis procedure yielded material partially ordered, while for Pr 3 + and Nd 3 + 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 PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + δ . For this compound the ionic conductivity at 800 °C was determined to be of the order of 0.03 S cm − 1 . • Cation order and disorder in LnBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + δ (Ln - Pr, Nd, Sm, Gd and Y) • Oxygen nonstoichiometry in LnBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + δ • Transport properties of LnBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5 + δ • Correlation between structure, oxygen nonstoichiometry and transport properties