A comprehensive investigation on structural, microstructural, optical, electrical, magnetic, and magnetoelectric (ME) properties of the single phase Bi4LaFeTi3−2x(WyCo2y)xO15 (0.00 ≤ x ≤ 0.15, y = 1.0) Aurivillius ceramics has been presented here. The preliminary x-ray diffraction and Raman spectroscopic studies reveal that a layered-structure perovskite Aurivillius phase of orthorhombic space group A21am. Furthermore, the surface morphology study provides a plate-like to spherical-like granules with increasing the dopant concentrations. The ferroelectric response prevails a slim P–E loop for pristine sample, whereas it provides the highest polarization (Ps) values of 7.21 and 13.25 μC/cm2 for x = 0.10 and 0.15 concentrations, respectively. At low temperature, magnetic measurements provide a weak antiferromagnetic ordering of pristine sample, whereas a strong FM (ferromagnetic) ordering of doped ceramics is attained. The observed strong FM behavior of the Aurivillius phase is attributed to either double exchange interactions between neighboring Fe3+–O–Fe3+, Co3+–O–Co3+, and Fe3+–O–Co3+ ions or antisymmetric Dzyaloshinskii–Moriya interactions for spin canting of adjacent sub-lattices via Co3+/2+–O–Co3+/2+, Fe3+–O–Fe3+, and Co3+/2+–O–Fe3+ ions. The temperature dependent dielectric broad-band spectroscopic study enlightened a dielectric relaxation. This is due to cationic disordering through the generation of oxygen vacancies, which yields a conduction mechanism at high temperature regions. Furthermore, a complex modulus spectroscopic technique is also adopted to investigate the dielectric relaxation at high temperature regimes. The observed magnetic ferroelectric polarization responses and magnitudes of ME coupling coefficients provided that this material could be useful for future magnetoelectric sensors.

The present work reports the analysis of temperature‐dependent electrical and conductivity studies on Ca2+ doped BiFeO3 multiferroic ceramics in the temperature range of 300–600 K. The effect of Ca2+ doping on the impedance and modulus behavior of BiFeO3 lattice is discussed. The observed changes as a function of increasing Ca2+ concentration have been explained using the change in crystal unit cell. It is also shown that the microstructure changes significantly as a function of Ca2+ concentration. The grain and grain boundary effects in determining the impedance behavior is also reported in the paper.

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The high leakage current in divalent ion doped BiFeO 3 systems is limiting their large scale application. It is clearly shown that the methodology of oxygen annealing will prove to be an effective procedure for suppressing the detrimental consequences that originate from the oxygen vacancies. The samples annealed under oxygen also show different particle morphologies and packing density that can help in tuning the relevant physical properties, viz., magnetic, ferroelectric, and magnetoelectric. The difference in magnetic behaviour in samples annealed in air and oxygen can be explained in terms of the modification in the Fe-O-Fe bonds, domain wall pinning centres, and crystal anisotropy. Another important observation is the stabilization of a dielectric anomaly near the magnetic transition temperature. This observation can make this multiferroic system very interesting for application in sensors where the change in the magnetic parameters can be observed by monitoring the electrical parameters. Detailed analysis of the dielectric and impedance curves indicate towards the presence of non-Debye type processes in samples obtained by annealing in air or oxygen. From the calculated activation energy values, the vacancy related relaxation mechanism is predominant in air annealed samples, while the oxygen annealed samples show the presence of two type of relaxation processes, viz., electron hopping mechanism stabilizes at low temperature while, at higher temperatures, the process associated with the diffusion of doubly ionized oxygen ions predominates. The ac-conductivity data suggests that the correlated barrier tunnelling mechanism, where single electron or two electrons hopping through neighbouring lattice sites leads to ac-conduction. V C 2014 AIP Publishing LLC.

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The solid solutions of (1Àx)Pb(Zr 0.65 Ti 0.35 )O 3 -xPb(Fe 2/3 W 1/3 )O 3 in different ratios were fabricated by a high-temperature solid-state reaction method using high-purity oxides for possible multiferroic applications. Structural analysis using x-ray diffraction powder patterns of the system by Rietveld refinement method exhibits the formation of rhombohedral phase with R3c space group. Detailed studies of dielectric permittivity as a function of temperature of the systems show that the frequency independent dielectric maximum temperature shifts toward room temperature on increasing x. In addition to this, the degree of diffuseness of the permittivity anomaly is more pronounced for higher content of Pb(Fe 2/3 W 1/3 )O 3 , implying the existence of a composition-induced diffuse phase transition for the limited range of compositional ratios. Detailed impedance spectroscopy analysis shows the contributions of grain, grain boundary, and interfacial polarizations in the resistive characteristics and conduction mechanism of the materials. The weak ferromagnetic and saturated ferroelectric loops indicate that system with x ¼ 0.1, 0.2 have good multiferroic characteristics, and may be useful for future spintronic devices. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4908222] 074105-2 Tirupathi et al. J. Appl. Phys. 117, 074105 (2015) FIG. 5. (a) and (b) Temperature dependent dielectric permittivity of (1 À x) Pb(Zr 0.65 Ti 0.35 )O 3 -xPb(Fe 2/3 W 1/3 )O 3 (x ¼ 0.1, 0.2). The red line in figure shows the fitted Curie-Weiss curve. 074105-4Tirupathi et al.