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 Fm3[combining macron]m. 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.

A new type of antiferrodistortive structure in a double perovskite with Pb

“…18 the dynamic distortions induced by the steroactive electron lone-pair of Pb 2+ . [14][15][16][17] Upon decreasing the temperature, two changes occur in the x-ray diffraction patterns below 390 K, as can be observed in Fig. 2.…”

“…The displacements may occur along either the [100] cubic direction as reported for Pb 2 CoWO 6 and Pb 2 MnWO 6 double perovskites 15,16 or the [111] cubic direction as in the Pb 2 ScSbO 6 compound. 17 In most cases, reported studies focused on electrical properties of samples with non-magnetic B-cations. Here, we report results of a study on Pb 2 MnReO 6 , where both Mn and Re have unpaired d electrons and the superexchange rules predict a ferrimagnetic ground state.…”

Synthesis and Crystal Structures of a Stable, a Metastable and a High Temperature Modification of Pb2NaIO6

“…Experimental details, structural data, and interatomic distances are given in Table 1, Table 2, and Table 3. The structure was tested for off‐center displacement as observed in high symmetry lead double perovskites2 and for B‐site disorder 3. No deviation from the conventional structure was observed.…”

“…At variance with the alkaline earth compounds, Pb 2+ has a 6s lone pair, so structural differences to the alkaline earth sodium periodates can be expected. The free electron pair is often responsible for the off‐centring in highly symmetric systems in order to reduce the electrostatic repulsion between Pb–O bonds and electron pair 2. This influence is also valid for B ‐disordered systems 3.…”

High-pressure synthesis, structural and complex magnetic properties of the ordered double perovskite Pb2NiReO6

“…The cubic (S. G. Fm3m) compounds are metallic or their resistivity show little changes with temperature; but the tetragonal (S. G. I4/m) and monoclinic (S. G. P2 1 /n) compounds present semiconducting and an insulating behavior respectively 11,12 . In addition, if a stereochemical active 6s 2 lone pair cation, such as Pb +2 is located at the A-position, it often induces strong anisotropy of the environment 13,14 that may create a polarization giving rise to dielectric, ferroelectric or piezoelectric properties [15][16][17] . Also, the insertion of Pb +2 at the A-site of the Sr 2 FeReO 6 semiconducting perovskite will lead to an expected decrease of the B-O-Re angle which will make Pb 2 NiReO 6 become insulator 18,19 .…”