Development of cost effective and efficient electrocatalysts is crucial to generate H2 as an alternative source of energy. However, expensive noble metal based electrocatalysts show best electrocatalytic performances which acts as main bottle-neck for commercial application. Therefore, non-precious electrocatalysts have become important for hydrogen and oxygen evolution reactions. Herein, we report the synthesis of high surface area (35 m2/g) sodium niobate nanoparticles by citrate precursor method. These nanoparticles were characterized by different techniques like X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic properties of cost-effective sodium niobate nanoparticles were investigated for HER and OER in 0.5 M KOH electrolyte using Ag/AgCl as reference electrode. The sodium niobate electrode showed significant current density for both OER (≈2.7 mA/cm2) and HER (≈0.7 mA/cm2) with onset potential of 0.9 V for OER and 0.6 V for HER. As-prepared sodium niobate nanoparticles show enhanced photocatalytic property (86% removal) towards the degradation of rose Bengal dye. Dielectric behaviour at different sintering temperatures was explained by Koop’s theory and Maxwell-Wagner mechanism. The dielectric constants of 41 and 38.5 and the dielectric losses of 0.04 and 0.025 were observed for the samples sintered at 500 °C and 700 °C, respectively at 500 kHz. Conductivity of the samples was understood by using power law fit.

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Electrocatalytic and Enhanced Photocatalytic Applications of Sodium Niobate Nanoparticles Developed by Citrate Precursor Route.

(BiFeO3–NaNbO3)–(P(VDF-TrFE)) co-polymer thin films were fabricated by spin coating technique and their electric, magnetic, electromechanical and magnetoelectric properties were investigated. In order to get the crystallization ‘β’ phase, the films have been annealed at 138 °C. The structural analysis of the films have been carried out using XRD, SEM, TEM, AFM, confocal Raman spectroscopy and FTIR spectroscopy which confirm the presence of BiFeO3 and NaNbO3 phases along with P(VDF-TrFE) crystalline phase. The magnetoelectric coupling measurements at room temperature confirm the multiferroic nature of the composite film with significant magnetoelectric coupling between BiFeO3, NaNbO3 and P(VDF-TrFE). The ME measurement gives a maximum coupling coefficient of 2.4 V cm−1 Oe−1 for the ceramic-polymer composite film which is two times higher than that of the ceramic alone. The higher piezoelectricity of the P(VDF-TrFE) (d33 > 20 pC/N) is expected to contribute to the enhancement in the electric and magnetic properties of the composite. The hysteresis loop observed at room temperature confirms the ferromagnetic property of the composite. The ultrahigh dielectric constant for 10 vol% of the ceramic in the polymer matrix with a low loss value (≈1) is a remarkable improvement. The resultant high dielectric permittivity, magnetoelectric coupling and ferromagnetic property at room temperature of these innovative nanocomposites make them particularly attractive for technological applications as storage energy materials.

Electric, magnetic, piezoelectric and magnetoelectric studies of phase pure (BiFeO3–NaNbO3)–(P(VDF-TrFE)) nanocomposite films prepared by spin coating

Electrical and nonlinear current-voltage characteristics of La-doped BiFeO3 ceramics

Nanocrystalline bismuth orthoferrite has been synthesized under conditions of glycine-nitrate combustion. Temperatures of activation of formation and growth of BiFeO3 nanocrystals have been shown to correlate with melting temperature of surface (non-autonomous) phases. Optimal temperature of synthesis of nanocrystalline bismuth orthoferrite has been determined.

Special features of formation of nanocrystalline BiFeO3 via the glycine-nitrate combustion method

The effect of Mo doping on the structural and dielectric properties has been investigated in detail for Co-Zn spinel ferrite. Solid state reaction technique has been used to prepare the CZMO. The structural analysis is performed using HRXRD technique which confirms the inverse spinel structure of the material. The frequency and temperature dependence of dielectric constant are studied which reveals that the dielectric dispersion is due to Maxwell-Wagner type polarization in agreement with Koop's phenomenological theory. The contribution of grain and grain boundary at high and low frequency respectively are evident in the dielectric constant. The variation of dielectric loss tangent with both the temperature and frequency has been studied. The room temperature and high frequency dielectric loss is observed to be very small. Also it is revealed that the dielectric loss tangent decreases with Mo substitution.

The effect of Mo doping on the structural and dielectric properties of Co-Zn ferrite

Single phase Bismuth ferrite (BiFeO3, BFO) nanoparticles (particle size ~ 50-100 nm) were synthesized by a novel chemical sol-gel technique. The detailed microstructural analysis has been performed through HRXRD, HRTEM and FESEM techniques. The nanoparticles are found to crystallize with distorted rhombohedral structure having R3c space group. The dielectric constant and tan δ loss are found to vary monotonically with temperature measured at different frequency ranging from 1 kHz to 1 MHz. The M (H) hysteresis behavior at 5 K reveals weak ferromagnetic nature of the BiFeO3 nanoparticles having coercivity (Hc) ~ 720 Oe and magnetization (Ms) ~ 1 emu/g at 5 T from SQUID measurements. The multiferroic character of BFO nanoparticles is confirmed through magnetoelectric response. The typical value of magnetodielectric response is observed to be 0.4% at 4300 Oe at room temperature at a frequency of 1 kHz. All the results suggest that the BFO nanoparticles are technologically very promising as far as magnetoelectric properties are concerned. Copyright © 2014 VBRI press.

B. Kumari

Papers

Magnetic, Magnetocapacitance And Dielectric Properties Of BiFeO3 Nanoceramics