Origin of large dielectric constant in La modified BiFeO3-PbTiO3 multiferroic

The presence of superlattice reflections and detailed analysis of the powder neutron and x-ray diffraction data reveals that La rich BLF-PT (BFO0.50–LF0.50)0.50–(PT)0.50 has a ferroelectric rhombohedral crystal structure with space group R3c at ambient condition. Impedance spectroscopy, dielectric spectroscopy is subset of impedance spectroscopy and ac conductivity measurements were performed in the temperature range 483 K ≤ T ≤ 573 K to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near TcFE. Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range (1 kHz ≤ f ≤ 10 MHz). It could be concluded that the grain boundaries are more resistive and capacitive as compared to the grains, resulting in inhomogeneity in the sample and cause broad frequency dependent dielectric transitions. The Maxwell-Wagner model fits very well up to ∼105 Hz. Enhancement in dielectric constant and remnant polarization values are possibly due to space charge polarization caused by piling of charges at the interface of grain and grain boundaries.