Structure and magnetic properties of a new anion-deficient perovskite Pb₂Ba₂BiFe₄ScO₁₃ with crystallographic shear structure

Graphical abstract: - Highlights: • Pb₂Ba₂BiFe₄ScO₁₃ was obtained by solid state synthesis. • Its structure was refined from combination of XPD and TEM. • It is a new member of the perovskite-related homologous series A_nB_nO_3n−2 with n = 5. • Pb₂Ba₂BiFe₄ScO₁₃ is antiferromagnetically ordered below T_N ≈350 K. - Abstract: Pb₂Ba₂BiFe₄ScO₁₃, a new n = 5 member of the oxygen-deficient perovskite-based A_nB_nO_3n−2 homologous series, was synthesized using a solid-state method. The crystal structure of Pb₂Ba₂BiFe₄ScO₁₃ was investigated by a combination of synchrotron X-ray powder diffraction, electron diffraction, high-angle annular dark-field scanning transmission electron microscopy and Mössbauer spectroscopy. At 900 K, it crystallizes in the Ammm space group with the unit cell parameters a = 5.8459(1) Å, b = 4.0426(1) Å, and c = 27.3435(1) Å. In the Pb₂Ba₂BiFe₄ScO₁₃ structure, quasi-two-dimensional perovskite blocks are periodically interleaved with ½[1 1 0] (1^¯01)_p crystallographic shear (CS) planes. At the CS planes, the corner-sharing FeO₆ octahedra are transformed into chains of edge-sharing FeO₅ distorted tetragonal pyramids. B-positions of the perovskite blocks between the CS planes are jointly occupied by Fe³⁺ and Sc³⁺. The chains of the FeO₅ pyramids and (Fe,Sc)O₆ octahedra delimit six-sided tunnels that are occupied by double columns of cations with a lone electron pair (Pb²⁺). The remaining A-cations (Bi³⁺, Ba²⁺) occupy positions in the perovskite block. According to the magnetic susceptibility measurements, Pb₂Ba₂BiFe₄ScO₁₃ is antiferromagnetically ordered below T_N ≈350 K