Structural, magnetic, and electrical properties of Bi_1-xLa_xMnO₃ (x=0.0, 0.1, and 0.2) solid solutions

Possible ferromagnetic and ferroelectric orders in ceramic Bi_1–xLa_xMnO₃ (x = 0.0, 0.1, and 0.2) samples prepared under 3–6 GPa pressure have been investigated. Rietveld fits to powder neutron diffraction data show that BiMnO₃ and Bi_0.9La_0.1MnO₃ adopt a monoclinic C2/c perovskite superstructure whereas Bi_0.8La_0.2MnO₃ has orthorhombic Pnma symmetry. Both structural analysis and Curie–Weiss fits to magnetic susceptibility data show that high spin d⁴ Mn³⁺ is present with no significant Bi deficiency or Mn⁴⁺ content apparent. La substitution suppresses the magnetic Curie temperature of the monoclinic phase from 105 K for x = 0 to 94 K at x = 0.1, but the x = 0.2 material shows antiferromagnetic order similar to that of LaMnO₃. Impedance spectroscopy and dielectric measurements on the x = 0.1 and 0.2 materials show modest bulk permittivity values (45–80) down to 50 K, and there is no strong evidence for ferroelectric behavior. The two samples have thermally activated conductivities with activation energies of 0.21–0.24 eV.