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In this work, Bi3+ doped Ba 0.98-3 x /2 Bi x Ca 0.02 Zr 0.02 Ti 0.976 Cu 0.008 O 3 [0 ≤ x ≤ 0.03] lead free ceramics, to be employed for structural, dielectric and ferroelectric studies, have been synthesized via conventional solid state reaction method. Rietveld refinement of the X-ray diffraction (XRD) data evidences the existence of a pure perovskite phase with tetragonal symmetry for all ceramics. The Scanning Electron Microscopy (SEM) reveals that the grain size, which is 16.14 μm for x = 0 reduced to 2.11 μm for x = 0.03. Dielectric studies demonstrate excellent dielectric behavior with high Curie temperature (T C ∼159 °C), high dielectric constant (ε r ∼834, ε max ∼ 3146), and a low dielectric loss (tanδ ∼ 0.019), for an optimum value of x = 0.02. The analysis of temperature coefficient of the dielectric permittivity indicates the applicability of these materials in multilayer ceramic capacitors. Impedance studies, conducted to understand the underlying physical mechanisms, are found to be in good agreement with the results of structural and dielectric studies. Furthermore, the ferroelectric measurement confirms the ferroelectric nature for all samples with an energy storage efficiency (η) of ∼42% for x = 0.02 composition. [ABSTRACT FROM AUTHOR]

Perovskite-type Ba0.98Ca0.02Zr0.02Ti0.98O3 (BCZT), Ba0.98Ca0.02Zr0.02Ti0.976Cu0.008O3 (BCZTC) and Ba0.9725Bi0.005Ca0.02Zr0.02Ti0.976Cu0.008O3 (BCZTCB) lead-free ceramics were synthesised via solid-state reaction method at a sintering temperature of 1380 °C. Effects of CuO and Bi2O3/CuO doping on structural, microstructural, dielectric and ferroelectric properties were investigated systematically. X-ray diffraction technique confirmed the existence of pure perovskite phase with the tetragonal structure in pure and in the doped BCZT ceramics at room temperature. The dielectric analysis demonstrated two anomalies around 24 °C and 126 °C for BCZT, which were identified as orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC) phase transition temperature, respectively. The TO-T temperature shifted to below 16 °C, while the TC increased to 132 °C for the BCZTCB sample. The physical mechanisms of the conduction processes were investigated through impedance spectroscopy, and the values of resistance, conductivity and activation energies associated with the grain and grain boundaries were evaluated. The activation energy was determined to be higher for doped samples than for pure BCZT. Further, the dopant-dependent ferroelectric nature of the ceramic samples was evidenced by the analysis of characteristic hysteresis loop, and a value of remnant polarization (Pr = 4.59 μC/cm2) was obtained for the BCZTCB ceramic sample. Furthermore, the d33 value, which was 54 pC/N for pure BCZT, was determined to be 140 pC/N and 64 pC/N for BCZTC and BCZTCB, respectively. [ABSTRACT FROM AUTHOR]

Perovskite-type bismuth ferrite (BiFeO3) multiferroic material is being considered as a potential candidate for magnetoelectric coupling and field-controlled multi-state memory applications. We report the Pr3+ and Lu3+ co-doping effect on the magnetoelectric coupling in BiFeO3 ceramics. In this study, Bi0.94Pr0.06FeO3 (BPO), Bi0.94Lu0.06FeO3 (BLO), and Bi0.94Pr0.03Lu0.03FeO3 (BPLO) ceramics were synthesized by conventional solid-state ceramic synthesis technique. The BPO sample displayed higher saturation magnetization as compared to BLO and BPLO samples which may be due to canting of spin cycloid of BFO and also due to the discrepancy between the antiparallel sublattice of Fe3+/Fe2+, the value of ferroelectric polarization of the BPO sample was found to be better than BLO and BPLO samples. However, the magnetocapacitance (MC) of the BPLO sample is found to be MC ~ 2.3% which is higher than that of BLO (MC ~ 1.4%) and BPO (MC ~ 1.7%) samples. In addition, the enhanced value of magnetoelectric coupling coefficient (αE) has been obtained for the BPLO sample. Overall, our results indicate that BPLO sample displays interesting magnetoelectric response for device applications. [ABSTRACT FROM AUTHOR]

Despite being of wide commercial use in devices, the orders of magnitude increase in resistance that can be seen in some semiconducting BaTiO3-based ceramics, on heating through the Curie temperature (TC), is far from well understood. Current understanding of the behavior hinges on the role of grain boundary resistance that can be modified by polarization discontinuities which develop in the ferroelectric state. However, direct nanoscale resistance mapping to verify this model has rarely been attempted, and the potential approach to engineer polarization states at the grain boundaries, that could lead to optimized positive temperature coefficient (PTC) behavior, is strongly underdeveloped. Here we present direct visualization and nanoscale mapping in a commercially optimized BaTiO3-PbTiO3-CaTiO3 PTC ceramic using Kelvin probe force microscopy, which shows that, even in the low resistance ferroelectric state, the potential drop at grain boundaries is significantly greater than in grain interiors. Aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy reveal new evidence of Pb-rich grain boundaries symptomatic of a higher net polarization normal to the grain boundaries compared to the purer grain interiors. These results validate the critical link between optimized PTC performance and higher local polarization at grain boundaries in this specific ceramic system and suggest a novel route towards engineering devices where an interface layer of higher spontaneous polarization could lead to enhanced PTC functionality. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline samples of single-phase co-doped (La3+, Lu3+) in Bi0.95− x La0.05Lu x FeO3 (x =0.03, 0.05 and 0.07) (grain size ∼0.5μm; tolerance factor ∼0.88) were prepared by solid state reaction of oxides, followed by rapid quenching of samples. Magnetic measurements show weak ferromagnetic-antiferromagnetism (WFM) nature at room temperature but ferromagnetic nature at ∼5K. Field cooled curves reveal spin reorientation in the system at lower temperature as shown by the peaks at ∼145 and ∼140K for x =0.03 and 0.07, respectively. Dielectric measurement shows relaxor type of phase transition for x =0.07. The magnetocapacitance was found to be enhanced (∼3 times than that of BiFeO3) due to co-doping of (La3+, Lu3+) in BiFeO3 ceramic showing the coupling effect between magnetic and electric behaviors which occurs through the lattice distortion. [Copyright &y& Elsevier]

Abstract: Optical, magnetocapacitance and dielectric properties of different composite films of BiFeO3–poly(vinylidene-fluoride) (with concentration of BiFeO3; 70, 60, 50 and 40wt%) are reported here for first time. The grain size was observed to be ∼50nm by using atomic force microscopy. A peak in refractive index appears at ∼455nm, which is found to be shifting towards lower wavelengths, while simultaneously the value of the optical energy band gap is found to increase with an increase in the concentration of PVDF in the composite. It was observed that PVDF, which works as matrix, increases the magnetocapacitance. The magnetocapacitance (MC) of BFO60 (BiFeO3; 60wt%) was found higher than Nb doped BiFeO3, which may be useful for device applications. [Copyright &y& Elsevier]