The high pressure perovskite PbCrO3 has been known since the 1960s but the electronic properties were controversial. The average structure is a cubic Pm-3m perovskite but a recent study revealed a charge ordering as Pb2+0.5Pb4+0.5Cr3+O3 with a ~3 x 3 x 3 Pb2+/Pb4+ ordered superstructure over small correlation lengths. A large pressure-induced volume collapse of 9.8% at ~2 GPa is due to a insulator-metal transition accompanying the charge transfer to high pressure configuration Pb2+Cr4+O3. Neutron diffraction is required to study structural and magnetic changes accompanying the unusual insulator to metal change in PbCrO3. Neutrons will show how TN (= 240 K at ambient P) changes with pressure, whether the G-type antiferromagnetism is suppressed at the transition, and whether the length scale for 3-fold local superstructure changes with pressure approaching the transition.
