Functional Transition Metal Perovskite Oxides with 6<i>s</i><sup>2</sup> Lone Pair Activity Stabilized by High-Pressure Synthesis
Masaki Azuma, Hajime Hojo, Kengo Oka, Hajime Yamamoto, Keisuke Shimizu, Kei Shigematsu, Yuki Sakai
Abstract
Perovskite ABO 3 oxides that have Bi and Pb at the A site and transition metals at the B site, when stabilized by high-pressure synthesis at several gigapascals, provide a rich parameter space of fascinating properties. Stereochemical 6 s 2 lone pairs of Bi 3+ and Pb 2+ induce polar or antipolar distortions. 6 s 2 and 6 s 0 (Bi 5+ and Pb 4+ ) charge degree of freedom enable intermetallic charge transfer transitions. The structural distortion and the charge degree of freedom are coupled with magnetism of transition metals, resulting in various functionalities. In particular, we highlight magnetization reversal by electric field and polarization rotation in BiFe 1− x Co x O 3 , negative thermal expansion in modified BiNiO 3 and PbVO 3 , and systematic charge distribution changes in Pb MO 3 ( M = 3 d transition metal).