Layered Oxychlorides [PbBiO2]An+1BnO3n–1Cl2 (A = Pb/Bi, B = Fe/Ti): Intergrowth of the Hematophanite and Sillen Phases

New layered structures corresponding
to the general formula [PbBiO2]­An+1BnO3n–1Cl2 were prepared.
Pb5BiFe3O10Cl2 (n = 3) and Pb5Bi2Fe4O13Cl2 (n = 4) are built as a stacking
of truncated An+1BnO3n–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 ≈ ap ≈ 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.

新型层状结构，其通式为[PbBiO2]­An+1BnO3n–1Cl2，已成功制备。Pb5BiFe3O10Cl2（n=3）与Pb5Bi2Fe4O13Cl2（n=4）由截顶的An+1BnO3n–1钙钛矿块与α-PbO型[A2O2]2+（A= Pb, Bi）块相结合，并嵌入氯层形成。这些结构块的交替排列可视为血影石与塞伦型结构块的共生。利用X射线和中子粉末衍射、透射电子显微镜及57Fe Mössbauer光谱，对Pb5BiFe3O10Cl2和Pb5Bi2Fe4O13Cl2的晶体结构与磁性结构进行了在1.5–700 K温度范围内的研究。两种化合物均以I4/mmm空间群结晶，其晶胞参数为a ≈ ap ≈ 3.92 Å（钙钛矿结构的晶胞参数），对于n=3的成员，c ≈ 43.0 Å；对于n=4的成员，c ≈ 53.5 Å。尽管含有Fe3+离子的板层之间距离较大（约14 Å），但在低于∼600 K的温度下，形成了长程反铁磁性序，Fe磁矩以G型排列，沿c轴对齐。通过制备Ti取代的n=4成员Pb6BiFe3TiO13Cl2，也证实了在这些结构的B亚晶格中可能存在d0和dn阳离子的混合。