Journal Article

Charge disproportionation and the pressure-induced insulator–metal transition in cubic perovskite PbCrO3

Uwatoko, Y., Shirako, Y., Goodenough, John B., Ding, Yang, Li, X., Hwang, G. S., Cheng, Jinguang, Larregola, S. A., Zhou, J.-S., Matsubayashi, K., Marshall, L. G., dos Santos, António M., Li, Z.-Y., Kweon, K. E., Suchomel, M. R.

2015

Overview

SignificanceThe steric activity of the lone pair electrons of Pb2+-containing compounds distorts the crystal structure and produces exotic physical properties. In ferroelectric PbTiO3 and PbVO3, the lone-pair electrons hybridizing with the oxygen lead to polarized MO6 octahedra. In PbRuO3, the hybridization induces unprecedented Pb-Ru bonds at high pressure. The sterochemical effect in PbCrO3 makes Pb bond with oxygen without a long-range periodicity. Under the influence of displaced Pb2+, Cr4+ undergoes a charge disproportionation that opens up a gap. In contrast to the pressure effect on PbTiO3 and PbRuO3, pressure restores the undistorted perovskite structure in PbCrO3. This result implies that the sterochemical effect of Pb2+ in a perovskite depends sensitively on the number and energy of the d electrons. The perovskite PbCrO3 is an antiferromagnetic insulator. However, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. We report a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. We argue that a charge disproportionation 3Cr4+ → 2Cr3+ + Cr6+ in association with the 6s-p hybridization on the Pb2+ is responsible for the insulating ground state of PbCrO3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT+U) calculations.

• Publisher: National Academy of Sciences
• Subject: Applied Physical Sciences / Physical Sciences