In situ X-ray and neutron diffraction of the Ruddlesden–Popper compounds (RE2−xSrx)0.98(Fe0.8Co0.2)1−yMgyO4−δ (RE=La, Pr): Structure and CO2 stability

The crystal structure of the Ruddlesden–Popper compounds (La1.0Sr1.0)0.98Fe0.8Co0.2O4−δ and (La1.2Sr0.8)0.98(Fe0.8Co0.2)0.8Mg0.2O4−δ was investigated at 1000 °C in N2 (aO2=1×10−4) by in-situ powder neutron diffraction. In-situ powder X-ray diffraction (PXD) was also employed to investigate the temperature dependence of the lattice parameters of the compounds in air and the oxygen activity dependence of the lattice parameters at 800 °C and 1000 °C. The thermal and chemical expansion coefficients, determined along the two crystallographic directions of the tetragonal unit cell, are highly anisotropic. The equivalent pseudo-cubic thermal and chemical expansion coefficients are in agreement with values determined by dilatometry. The chemical stability in CO2 containing environments of various Ruddlesden–Popper compounds with chemical formula (RE2−xSrx)0.98(Fe0.8Co0.2)1−yMgyO4−δ (RE=La, Pr), as well as their stability limit in H2/H2O=4.5 were also determined by in-situ PXD for x=0.9, 1.0 and y=0, 0.2.

Influence of electronic configuration on bond length, lattice parameters and anisotropic thermal and chemical expansion.Figure optionsDownload as PowerPoint slideHighlights
► The thermal and chemical expansion coefficients are largely anisotropic.
► The expansion of the perovskite layers is constrained along the a direction.
► The studied compositions show remarkable thermodynamic stability upon reduction.
► The thermal and chemical expansion coefficients are lower than related perovskites.
► The investigated materials decompose in CO2 containing atmospheres.