Layered oxychlorides [PbBiO₂]A_n+1B_nO_3n-1Cl₂ (A = Pb/Bi, B = Fe/Ti): Intergrowth of the hematophanite and sillen phases

New layered structures corresponding to the general formula [PbBiO₂]A_n+1B_nO_3n-1Cl₂ were prepared. Pb₅BiFe₃O₁₀Cl₂ (n = 3) and Pb₅Bi₂Fe₄O₁₃Cl₂ (n = 4) are built as a stacking of truncated A_n+1B_nO_3n-1 perovskite blocks and α-PbO-type [A₂O₂]²⁺ (A = Pb, Bi) blocks combined with chlorine sheets. The alternation of these structural blocks can be represented as an intergrowth between the hematophanite and Sillen-type structural blocks. The crystal and magnetic structures of Pb₅BiFe₃O₁₀Cl₂ and Pb₅Bi₂Fe₄O₁₃Cl₂ were investigated in the temperature range of 1.5-700 K using X-ray and neutron powder diffraction, transmission electron microscopy and ⁵⁷Fe Mössbauer spectroscopy. Both compounds crystallize in the I4/mmm space group with the unit cell parameters a ≈ a_p ≈ 3.92 Å (a unit-cell parameter of the perovskite structure), c ≈ 43.0 Å for the n = 3 member and c ≈ 53.5 Å for the n = 4 member. Despite the large separation between the slabs containing the Fe³⁺ ions (nearly 14 Å), long-range antiferromagnetic order sets in below ∼600 K with the G-type arrangement of the Fe magnetic moments aligned along the c-axis. The possibility of mixing d⁰ and dⁿ cations at the B sublattice of these structures was also demonstrated by preparing the Ti-substituted n = 4 member Pb₆BiFe₃TiO₁₃Cl₂.