Strengthened relaxor behavior in (1-x)Pb(Fe0.5Nb0.5)O3-xBiFeO3

A systematic study of (1-x)Pb(Fe0.5Nb0.5)O-3-xBiFeO(3) (x = 0-0.5) was performed by combining dielectric and electromechanical measurements with structural and microstructural characterization in order to investigate the strengthening of the relaxor properties when adding BiFeO3 into Pb(Fe0.5Nb0.5)O-3 and forming a solid solution. Pb(Fe0.5Nb0.5)O-3 crystalizes in monoclinic symmetry exhibiting ferroelectric-like polarization versus electric field (P-E) hysteresis loop and sub-micron-sized ferroelectric domains. Adding BiFeO3 to Pb(Fe0.5Nb0.5)O-3 favors a pseudocubic phase and a gradual strengthening of the relaxor behavior of the prepared ceramics. This is indicated by a broadening of the peak in temperature-dependent permittivity, narrowing of P-E hysteresis loops and decreasing size of ferroelectric domains resulting in polar nanodomains for x = 0.20 composition. The relaxor behavior was additionally confirmed by Vogel-Fulcher analysis. For the x >= 0.30 compositions, broad high-temperature anomalies are observed in dielectric permittivity versus temperature measurements in addition to the frequency-dispersive peak located close to room temperature. These samples also exhibit pinched P-E hysteresis loops. The observed pinching is most probably related to the reorganization of polar nanoregions under the electric field as shown by synchrotron X-ray diffraction measurements as well as by piezo-response force microscopy analysis, while in part affected by the presence of charged point defects and anti-ferroelectric order, as indicated from rapid cooling experiments and high-resolution transmission electron microscopy, respectively.