High-pressure synthesis and pressure-induced spin, charge and lattice transitions of PbCoO₃

By using a peculiar high-pressure and high-temperature method, we for the first time prepared PbCoO₃ [1]. It crystallizes into an A-site and B-site ordered quadruple perovskite structure with space group of Pn-3. The charge combination is confirmed to be Pb²⁺Pb⁴⁺₃Co²⁺₂Co³⁺₃O₁₂, where the Co²⁺ is high spin while the Co³⁺ is low spin. Although only Co²⁺ is magnetic, the compound experiences two antiferromagnetic transitions. More interestingly, when external pressure is applied, the high spin Co²⁺ gradually changes to low spin with pressure up to 15 GPa. Between 15 and 30 GPa, the intermetallic charge transfer occurs between Pb⁴⁺ and Co²⁺. The accumulated charge-transfer effect triggers a metal-insulator transition as well as a first-order structural phase transition toward a Tetra.-I phase at ~20 GPa near room temperature. On further compression over 30 GPa, the charge transfer completes, leading to another first-order structural transformation toward a Tetra.-II phase and the reentrant electrical insulating behavior.

[1] Y. Sakai et al, J. Am. Chem. Soc. 139, 4574 (2017).