Vibrational, magnetic, and dielectric behavior of La-substituted BiFeO3-PbTiO3

Phonons and magnetic and ferroelectric ordering in La-substituted (Bi1-xLax)(0.5)Pb0.5Fe0.5Ti0.5O3 for samples with 0.0 <= x <= 0.5 are investigated using Raman, magnetization, and polarization measurements as a function of temperature. The system is tetragonal for pure Bi0.5Pb0.5Fe0.5Ti0.5O3 with a large c/a ratio. The anisotropy is reduced when Bi is partially replaced by La (0 <= x <= 0.5), and it turns cubic for x >= 0.4. All the properties are found to change significantly with changes in the c/a ratio. Evidence of spin-glass-like magnetic ordering at low temperature is found in the case of x - 0.2. A mechanism for the systematic change of magnetic ordering temperature as a function of doping is also discussed. The phonon frequencies and line widths exhibit discontinuous changes across the tetragonal-cubic transition. Large polarization and forbidden Raman scattering in the cubic phase are explained on the basis of symmetry breaking due to the formation of a polar nano region, which leads to relaxor behavior. (C) 2011 American Institute of Physics. [doi:10.1063/1.3673240]