Neutron structural characterization and transport properties of oxidized and reduced La0.5Sr0.5M0.5Ti 0.5O3 (M = Mn, Fe) perovskites: Possible electrode materials in solid-oxide fuel cells

摘要

Oxygen-stoichiometric La0.5Sr0.5M 0.5Ti0.5O3 (M Mn, Fe) perovskites and the corresponding reduced specimens, of La0.5Sr0.5M 0.5Ti0.5O3-δ composition, have been prepared and characterized by x-ray diffraction and neutron powder diffraction (NPD), in complement with thermal analysis, electrical conductivity, and thermal expansion measurements. NPD data show that these perovskites are all orthorhombic, space group Pbnm (No. 62). The total reduction of M3 to M2 in the reduced phases is accompanied with the occurrence of oxygen vacancies, which was confirmed by thermogravimetric analysis (TGA). Above room-temperature, these phases undergo two structural phase transitions studied in situ from NPD data; the former to a tetragonal (I4/mcm) structure, and the second one to a cubic (Pm-3m) phase. All the oxides display a semiconductor-like behavior with a maximum conductivity value of 15 S·cm-1 for the oxidized La0.5Sr0.5Mn0.5Ti 0.5O3 phase at 850 °C. The measured thermal expansion coefficients perfectly match with the values usually displayed by solid-oxide fuel cell (SOFC) electrolytes. The obtained results present these perovskites as alternative electrodes for SOFCs. © 2013 American Institute of Physics.