Strengthened relaxor behavior in (1−x)Pb(Fe0.5Nb0.5)O3–xBiFeO3†
A systematic study of (1−x)Pb(Fe0.5Nb0.5)O3–xBiFeO3 (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)O3 and forming a solid solution. Pb(Fe0.5Nb0.5)O3 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)O3 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.