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In order to tailor the multiferroic as well as dielectric properties, we have synthesized BiFeO3 (BFO) and Ni-doped BFO nanoparticles of composition BiFe1-xNixO3 (0 ≤ x ≤ 0.07) via the sol-gel method. The influence of Ni-doping at the Fe site of BiFeO3 on the structural, dielectric, and multiferroic properties was investigated via various characterization techniques such as Raman spectroscopy, vibrating sample magnetometer, polarization-electric field (P-E) loop tracer, and LCR meter. The Raman spectra reveal the rhombohedral distorted perovskite structure of the samples in the R3c space group. The frequency dependent dielectric measurements at room temperature show that the dielectric constant for the pristine sample is an order of magnitude lower than the 1% Ni-doped BFO sample. It is also evident that the ac conductivity increases with the increase in frequency as well as Ni content. Further, the universal dielectric response (UDR) phenomenon is responsible for the dielectric behavior of all the samples in the whole frequency range except for the BiFeO3 and BiFe0.97Ni0.03O3 samples. These samples exhibit deviation from UDR phenomenon at higher frequencies. The room temperature hysteresis (M-H) loops exhibit the saturation in magnetization at higher magnetic fields. The result demonstrates a significant influence on the saturation magnetization with the Ni doping in BFO, prompting the ferromagnetic nature of the samples. The saturation magnetization of the 7% Ni-doped sample is approximately six times higher than the pristine one. The saturated P-E hysteresis loops establish the ferroelectric nature of the synthesized samples that are enhanced significantly on Ni doping. Thus, the doping of Ni in BiFeO3 improves the multiferroic properties of the matrix. [ABSTRACT FROM AUTHOR]

Polycrystalline Pr0.8Ca0.2MnO3 has been synthesized through solid state reaction route and phase purity is analyzed using synchrotron XRD. Magnetization M(T) showed Mn spin alignment due to ferromagnetic ordering around 125 K (TC), whereas M(H) showed an onset of non-linear behavior from 200 K and with temperature re-orientation of magnetic moment is discussed. The modulation of relaxation processes revealed different formations of impedance plane plots with temperatures. A change in equivalent circuit models from (R1C1)(R2Q2) to (R1C1)(R2Q2)(R3Q3) at 100 K is being reported. The analysis of the impedance data is carried out by calculating impedance of grains and grain boundaries. Fitted parameters derived from these equivalent circuit parameters showed a change in conduction mechanism from small polaronic hopping model (SPH) to Mott's variable range hopping (MVRH) model, around 125 K (TC). Carriers hop to larger distance with multiple activation energies and are described by MVRH below TC. Above this temperature, different trap centers start facilitating these carriers through SPH. Dielectric relaxation shows dispersion around 125 K and the origin of this polarization lies close to the relaxation derived from the grains and their interfaces. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic and electrical response of the sol-gel synthesized NiFe2O4 nanoparticles. Changes in the impedance plane plots with temperature have been discussed and correlated to the microstructure of the material. Thermally activated hopping carriers between Fe3+-Fe2+ and Ni2+-Ni3+ ions have been determined for a decrease in the resistance of the sample and a change in the conduction mechanism around 318 K. The mixed spinel structure and broken exchange bonds due to small size effects are due to the canted spin structure at the surface of the nanoparticles. The magnetization is found to be influenced by the surface spin canting and anisotropy. We have established the semiconducting to metallic transition (SMT) temperature to be around 358 K in terms of localized and delocalized eg electrons along with a transition from less conductive [Fe3+-O2--Fe3+] and [Ni2+-O2--Ni2+] linkage to more conductive [Fe3+-Fe2+] and [Ni2+-Ni3+] linkage at the octahedral B site. A decrease in the dielectric constant with temperature has been discussed in terms of the depletion of space charge layers due to the repulsion of delocalized eg electrons from the grain boundary planes. The anomalies in tangent loss and conductivity data around 358 K are discussed in the context of the SMT. [ABSTRACT FROM AUTHOR]

In this work, we address the issue of microstructural changes in the electrical properties of charge ordered polycrystalline La0.50Ca0.50MnO3+δ sample during thermal cycling through impedance spectroscopy. The modulations of relaxation time with temperatures and different thermal cycling shows different magnitudes of impedance plane plots. Thermal cycling induces varying mechanical and electrical stresses in the grains and in the grain boundaries, changing the resistance of the grains (R1) and the grain boundaries (R2) by changing the boundary potentials and trap state scattering cross sections. At metal-insulator transition temperature (MIT), R1 increases with polynomial first order and R2 increases with polynomial second order. The values of R1 and R2 show different orders of variations along with reversible and irreversible behaviors around and below MIT. We report a method by virtue of which charge ordering temperature TCO has been determined with the change in the magnitude of grain boundary resistance by thermal cycling. Localization of charge carriers in the traps with thermal cycling around MIT and delocalization of charge carriers with different frequencies have been discussed. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy has been employed to investigate the microscopic nature of the charge/orbital ordering (COO) in polycrystalline La0.50Ca0.50MnO3+δ sample at different temperatures. The modulations of relaxation time with temperatures show different behaviors of Z′ and Z″. An equivalent circuit model (R1C)(R2Q) has been employed to investigate the electrical parameters of La0.50Ca0.50MnO3+δ at different temperatures. The resistance of grain and grain boundaries shows maxima at metal-insulator (MI) transition temperature (≈153 K). Three temperature zones have been identified. In the first temperature zone which has been from 85 to 140 K, below MI transition temperature, melting of COO with strong Jahn–Teller (JT) distortions has been reported. In the second zone, around MI transition temperature, melting and collapse of COO with weak JT distortion result in colossal drop in Z′. In the third temperature zone, above MI transition temperature, charge ordering (CO) around 203 K and onset of short range CO at 253 K have been determined. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy is used for addressing the issue of microstructural changes in the electrical properties of charge ordered polycrystalline [La.sub.0.50][Ca.sub.0.50]Mn[O.sub.3+[delta]] sample during thermal cycling. The values of the resistance of the grains and the grain boundaries have shown different orders of variations along with reversible and irreversible behaviors around and below metal-insulator transition temperature (MIT).

The impedance spectroscopy is used to examine the microscopic nature of the charge/orbital ordering (COO) in polycrystalline [La.sub.0.50][Ca.sub.0.50]Mn[O.sub.3+[delta]] sample at different temperatures. The anomalies in the depression angles of impedance plane plots are compared with the macrostructure of the material.

Polycrystalline Pr0.5-xLaxCa0.5MnO3 (x = 0.0-0.40) ceramics are synthesized by conventional solid state reaction method, and phase purity is confirmed by employing X-ray diffraction. Temperature dependent ac impedance spectroscopic measurements enable us to determine an increasing trend in resistance values of these samples with the decrease in temperatures. However, a decreasing trend in resistance values with increase in the La-doping at Pr-site is observed. A metal to insulator transition (MIT) is reported for x ≥ 0.2, which is shifted to higher temperature values with further increase of x doping. Two equivalent circuit models, i.e., (ReQe)(RgbQgb) and (ReQe)(RgbQgb)(RgQg) are employed to explain the impedance data with and without MIT, respectively. Mott variable range hopping model is found to be an appropriate model for defining the conduction mechanism of charge carriers in the semiconducting region. The decrease in the impedance with x doping is explained in terms of increase in the localization length obtained from the fitting of Rgb. Using tanδ results, thermally activated relaxation behavior is discussed for x = 0.0 and 0.1; whereas for x = 0.2, a temperature independent relaxation behavior is conferred due to the change in the hopping process of charge carriers. [ABSTRACT FROM AUTHOR]