The role of the Pb2+ 6s lone pair in the structure of the double perovskite Pb2ScSbO6

Abstract

The new double perovskite Pb₂ScSbO₆ was synthesized by standard ceramic procedures; the Rietveld refinement of room temperature neutron powder diffraction data shows that the crystal structure is well defined in the space group Fmm. It contains a completely ordered array of alternating ScO₆ and SbO₆ octahedra sharing corners; the PbO₁₂ polyhedra present an off-center displacement of the lead atoms along the [111] direction, due to the electrostatic repulsion between the Pb²⁺ 6s lone pair and the Pb–O bonds of the cuboctahedron. Dielectric permittivity measurements show a peak near 343 K, with a Curie–Weiss response above this temperature, which suggests an antiferroelectric behavior. Finally we present a DFT study of the electronic structure of Pb₂ScSbO₆, showing a great difference between the electronic density within SbO₆ and ScO₆ octahedra.