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Because of the possible crossover of Pb and 3d transition-metal (TM) redox levels, a charge transfer between Pb and TMleads to a continuous evolution from Pb2+Ti4+O3to Pb4+Ni2+O3in the perovskite family of PbTMO3as verified by several reports. However, very little information is known about PbMnO3in the PbTMO3series. The perovskite PbMnO3is the most difficult one to synthesize, although its geometric tolerance factor is close to 1. Here, we report a careful study of PbMnO3synthesized under 15 GPa by a structural refinement and high-precision X-ray absorption spectroscopy (XAS) as well as a variety of measurements of physical properties. We can rationalize the physical properties of PbMnO3based on a local bonding model and the valence states of Pb and Mn from XAS. Moreover, the complete study of PbMnO3allows us to construct a more consistent picture of the valence evolution and the charge disproportionation for the entire family of PbTMO3perovskites.

Spin state transitions and intermetallic charge transfers can essentially change material structural and physical properties while excluding external chemical doping. However, these two effects have rarely been found to occur sequentially in a specific material. In this article, we show the realization of these two phenomena in a perovskite oxide PbCoO3with a simple ABO3composition under high pressure. PbCoO3possesses a peculiar A- and B-site ordered charge distribution Pb2+Pb4+3Co2+2Co3+2O12with insulating behavior at ambient conditions. The high spin Co2+gradually changes to low spin with increasing pressure up to about 15 GPa, leading to an anomalous increase of resistance magnitude. Between 15 and 30 GPa, the intermetallic charge transfer occurs between Pb4+and Co2+cations. 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 the onset of ∼20 GPa near room temperature. On further compression over 30 GPa, the charge transfer completes, giving rise to another first-order structural transformation toward a Tetra.-II phase and the reentrant electrical insulating behavior.

The phase instability of bismuth perovskite (BiMO3), where M is a ferromagnetic cation, is exploited to create self‐assembled magnetic oxide nanocrystal arrays on oxide supports. Conditions during pulsed laser deposition are tuned so as to induce complete breakdown of the perovskite precursor into bismuth oxide (Bi2O3) and metal oxide (M‐Ox) pockets. Subsequent cooling in vacuum volatizes the Bi2O3leaving behind an array of monodisperse nanocrystals. In situ reflective high energy electron diffraction beam is exploited to monitor the synthesis in real‐time. Analysis of the patterns confirms the phase separation and volatization process. Successful synthesis of M‐Ox, where M = Mn, Fe, Co, and Cr, is shown using this template‐free facile approach. Detailed magnetic characterization of nanocrystals is carried out to reveal the functionalities such as magnetic anisotropy as well as larger than bulk moments, as expected in these oxide nanostructures.

In this study, advanced control of crystallographic orientations and magnetic properties of self-assembled nanostructures viarational selections of substrates is demonstrated. We show that in the perovskite−spinel BiFeO3−CoFe2O4model system the crystal orientation of self-assembled CoFe2O4nanopillars can be tuned among (001), (011), and (111), while that of the BiFeO3matrix is fixed in (001). Moreover, the resultant CoFe2O4nanopillars appear in various shapes: pyramid, roof, and triangular platform, respectively. The tunable nanostructures through this approach enable the control of material functionality such as the magnetic anisotropy of CoFe2O4. This study opens a new pathway for the engineering of self-assembled heteroepitaxial nanostructures.