Synthesis, Structural Transformation, Thermal Stability, Valence State, and Magnetic and Electronic Properties of PbNiO_3 with Perovskite-and LiNbO_3-Type Structures

摘要

We synthesized two high-pressure polymorphs PbNiO_3 with different structures, a perovskite-type and a LiNbO_3-type structure, and investigated their formation behavior, detailed structure, structural transformation, thermal stability, valence state of cations, and magnetic and electronic properties. A perovskite-type PbNiO_3 synthesized at 800 ℃ under a pressure of 3 GPa crystallizes as an orthorhombic GdFeO_3-type structure with a space group Pnma. The reaction under high pressure was monitored by an in situ energy dispersive X-ray diffraction experiment, which revealed that a perovskit-type phase was formed even at 400 ℃ under 3 GPa. The obtained perovskite-type phase irreversibly transforms to a LiNbO_3-type phase with an acentric space group R3c by heat treatment at ambient pressure. The Rietveld structural refinement using synchrotron X-ray diffraction data and the XPS measurement for both the perovskite- and the LiNbO_3-type phases reveal that both phases possess the valence state of Pb~(4+)Ni~(2+)O_3. Perovskite-type PbNiO_3 is the first example of the Pb M~(2+)O_3 series, and the first example of the perovskite containing a tetravalent A-site cation without lone pair electrons. The magnetic susceptibility measurement shows that the perovskite- and LiNbO_3-type PbNiO_3 undergo anriferromagnetic transition at 225 and 205 K, respectively. Both the perovskite- and LiNbO_3-type phases exhibit semiconducting behavior.