High pressure synthesis and properties of Bi0.5Pb0.5CrO3: A novel Cr4+/Cr3+ perovskite

We have synthesized a new Bi0.5Pb0.5CrO3 perovskite phase by means of a high pressure reaction at 70 kbar and 1000 degrees C. The distorted orthorhombic perovskite structure can be indexed in the space group Pnma with lattice parameters a=5.4768 (I) angstrom, b=7.7450 (2) angstrom, and c =5.4574 (1) angstrom at room temperature, but undergoes a structural phase transition and enters into a P2(1)/m monoclinic distorted perovskite phase below 150 K with a=5.4173 (2), 6=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 approximate to 40K. The semiconducting-type electrical resistivity is relatively low, associated with Cr3+/Cr4+ electron hopping, and shows considerable magneto-resistance (up to 15%). Due to the low resistivity the dielectric permittivity epsilon(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. (C) 2014 Elsevier Inc. All rights reserved.