Relationship between Pb ion off-centering and lone pair electrons.

Abstract

High-pressure synthesized Pb-based perovskites exhibit diverse functional properties. PbCrO₃, for instance, displays distinctive diffuse scattering and valence skipping, forming Pb²⁺ and Pb⁴⁺ ions. However, the spatial distribution of Pb ions in the crystal remains largely unexplored. Here, we elucidate the role of Pb ions with different valences through Sr substitution, using high-resolution transmission electron microscopy combined with elemental mapping. This approach allows us to accurately examine the distribution of Sr and Pb ions in the same atomic columns. The results reveal that in Pb_0.8Sr_0.2CrO₃, Sr ions occupy a squared lattice, while Pb ions exhibit positional distortions. Simulations based on the experimentally determined Pb distribution reproduce the diffuse scattering observed in PbCrO₃. These findings suggest that the lone pair electrons of s orbitals are responsible for the local lattice distortion. Our study provides atomistic insights into the local structures of materials exhibiting valence skipping.