Correlation between structural, magnetic and ferroelectric properties of Fe-doped (Ba-Ca)TiO3 lead-free piezoelectric

Abstract

The effect of iron (Fe) doping modification on the structure and properties of Ba0.92Ca0.08TiO3 (BCT8) lead-free ferroelectrics is investigated in detail. Intrinsic BaTiO3 (BT) and Ba0.92Ca0.08TiO3 (BCT8) lead-free polycrystalline ceramics were synthesized by conventional solid-state chemical reaction method. The crystal structure, morphology, chemical composition and valence state, magnetic and ferroelectric properties of BCT8 ceramics were evaluated as a function of variable Fe-content (0–5 wt%). X-ray diffraction measurements coupled with Rietveld refinement analyses indicate that the BT, BCT8, and Fe-BCT8 ceramics crystallize in single phase tetragonal structure. Phase transformation occurs with higher Fe doping; Fe-BCT8 ceramics with 5 wt% Fe exhibits fully transformed orthorhombic structure. The crystal structure and phase formation of these ceramics was further confirmed by the Raman spectroscopic (RS) measurements. The RS data coupled with high-resolution X-ray photoelectron spectroscopic (XPS) analyses also confirm the formation of single phase materials without any presence of secondary or impurity phases. Microstructure imaging analyses indicate that the grain size was ∼1 μm, while agglomeration and inhomogeneous distribution were observed with Fe doping. Polarization-electric field (P-E) hysteresis and strain-electric field (S-E) hysteresis measurements revealed the ferroelectric and piezoelectric nature of the ceramics. Ferroelectric and piezoelectric properties were observed to be suppressed for Fe doped BCT8 ceramics due to the partial replacement of Ti4+ by Fe3+ as confirmed by the chemical analyses made using XPS. Temperature dependent dielectric measurements for Fe doped BCT8 show a drastic decrease in ferroelectric Curie temperature (Tc), along with a decrease in dielectric constant compared to that of undoped BCT8. Magnetization (M-H) measurements confirm the presence of long-range magnetic ordering for 5% Fe-doped BCT8 sample. The results demonstrate that addition of 5% Fe in lead-free BCT8 perovskite induces the magnetic ordering and a switchable ferroelectric state, which evidences the presence of multiferroic nature that can be used for four-bit memory and switching applications.