High pressure synthesis and properties of Bi{sub 0.5}Pb{sub 0.5}CrO{sub 3}: A novel Cr{sup 4+}/Cr{sup 3+} perovskite

We have synthesized a new Bi{sub 0.5}Pb{sub 0.}5CrO{sub 3} perovskite phase by means of a high pressure reaction at 70 kbar and 1000 °C. The distorted orthorhombic perovskite structure can be indexed in the space group Pnma with lattice parameters a=5.4768 (1) A, b=7.7450 (2) A, and c=5.4574 (1) A at room temperature, but undergoes a structural phase transition and enters into a P2{sub 1}/m monoclinic distorted perovskite phase below 150 K with a=5.4173 (2), b=7.7286 (4) and c=5.4930 (3). The structural transition is coincident with the onset of magnetic interactions. At lower temperatures a weak ferromagnetic structure is evident related to antiferromagnetic Cr-spin canting and a spin-glass transition is observed at ≈40 K. The semiconducting-type electrical resistivity is relatively low, associated with Cr{sup 3+}/Cr{sup 4+} electron hopping, and shows considerable magneto-resistance (up to 15%). Due to the low resistivity the dielectric permittivity e{sub r} could be determined only below T<80 K to be ≈300 and did not show any strong temperature-dependence. Ferroelectricity was not detected in the T-range investigated and no magnetocapacitance effects were observed. - Graphical abstract: A new Bi{sub 0.5}Pb{sub 0.}5CrO{sub 3} perovskite phase has been synthesized under high pressure (70 kbar) and high temperature (1000 °C)more » conditions. The room temperature structure is orthorhombic and can be indexed in the space group Pnma but below 150 K undergoes a structural phase transition and enters into a P2{sub 1}/m monoclinic distorted perovskite phase. The structural transition is coincident with the onset of magnetic interactions. Mott variable-range hopping charge transport and magnetoresistance effects are evident. - Highlights: • A new Bi{sub 0.5}Pb{sub 0.}5CrO{sub 3} perovskite has been synthesized under HP/HT conditions. • An orthorhombic-to monoclinic phase transition takes place at 150 K. • The structural transition is coincident with the onset of magnetic interactions. • Mott variable-range hopping charge transport and magnetoresistance are evident.« less