Phase transition and enhanced magneto-dielectric response in BiFeO3-DyMnO3 multiferroics

This work is partially supported by DST fast track Project No. SR/FTP/PS-16/2009. Dhiren K. Pradhan acknowledges IFN (NSF Grant No. EPS—01002410) for fellowship. The work at UPR was supported by National Science Foundation (NSF DMR 1410869) and Institute for Functional Nanomaterials (IFN).We report systematic studies on crystal structure and magneto-dielectric properties of (1 − x) BiFeO3-x DyMnO3 (0.0 ≤ x ≤ 0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn21a at x = 0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO3 substitution. Magneto-impedance spectroscopy reveals a significant change (∼18%) in dielectricpermittivity at H = 2 T for x = 0.2.Peer reviewe

Synthesis and characterization of SmFeO3 and its effect on the electrical and energy storage properties of PVDF

Here we report an anomalous electrical properties and energy storage performance of SmFeO3-Poly(vinylidene fluoride) (SFO-PVDF) composites fabricated by a simple solvent casting technique with SmFeO3 concentration varying from 1 to 10 wt% with respect to PVDF content. Dielectric permittivity and ferroelectric parameters of PVDF initially decreased for 1 wt% SmFeO3 incorporation and then started increasing with further increase of SFO concentration. However, in contrary to our expectation, all the composites exhibited lower values of dielectric permittivity compared to neat PVDF. The observed unexpected trend of variation of dielectric permittivity and electric displacement was explained by considering a local electric field approximation model followed by the mechanism of polymer chain movement and dipole orientation of PVDF

Preparation and characterization of PMN-PT nanocomposite

111-115Ferroelectric ceramic-polymer composites are considered as promising materials for applications in sensors, actuators and hydrophones. They are attractive for application as they exhibit high piezoelectric and pyroelectric response, low acoustic impedance matching with water and human skin and their properties can be tailored to various requirements. The advantage of composites over conventional ceramics is that they have better mechanical shock resistance and more durable. Lead magnesium niobate-lead titanate (PMN-PT with 35 mol% PT) ceramic powder is fabricated by citrate gel method. The calcinations temperature is optimized by thermal analysis. The formation of the ceramic powder is confirmed by XRD. The microstructural properties have been studied by, SEM and TEM. The particle size calculated from TEM was found to be between 50-55 nm and the homogeneous distribution of the powders was also observed. The composites have been prepared using solvent casting in which the powder is dispersed homogeneously in the polymer matrix. Different composites are made by varying the ceramic to polymer ratio. The structural, microstructural properties of the composite are studied

Investigation of density of states and electrical properties of Ba0.5Co0.5Bi2Nb2O9 nanoceramics prepared by chemical route

Barium-cobalt-bismuth-niobate, Ba0.5Co0.5Bi2Nb2O9 (BCoBN) nanocrystalline ferroelectric ceramic was prepared through chemical route. XRD analysis showed single phase layered perovskite structure of BCoBN when calcined at 650 A degrees C, 2 h. The average crystallite size was found to be 18 nm. The microstructure was studied through scanning electron microscopy. The dielectric and ferroelectric properties were investigated in the temperature range 50-500 A degrees C. The dielectric constant and dielectric loss plot with respect to temperature both indicated strong relaxor behavior. Frequency versus complex impedance plot also supported the relaxor properties of the material. The impedance spectroscopy study showed only grain conductivity. Variation of ac conductivity study exhibited Arrhenius type of electrical conductivity where the hopping frequency shifted towards higher frequency region with increasing temperature. The ac conductivity values were used to evaluate the density of state at the Fermi level. The minimum hopping distance was found to be decreased with increasing temperature

Ethanol sensing evaluation of sol-gel barium calcium ferrite

Hexaferrites are very attractive materials for high-frequency circuits and operating devices, nevertheless their use for sensing application is very rare. In the present work, BaCa2Fe16O27 hexaferrite was synthesized by a simple sol-gel technique. Structural and microstructural information have been obtained by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The gas sensing performance of BaCa2Fe16O27 hexaferrite-based sensors was investigated for the detection of some common volatile organic compounds and gases like ethanol, acetone, methane and carbon monoxide. The results showed the sensors to exhibit high sensitivity, quick response/recovery and good reproducibility and stability towards 100 ppm ethanol. Moreover the sensors proved to be highly selective from measurements of cross sensitivity. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Enhancement in energy storage and piezoelectric performance of three phase (PZT/MWCNT/PVDF) composite

The conversion of mechanical energy (vibration) to electrical signal (voltage/power) is one of the versatile phenomena in energy harvesting process. In the effort to develop self-powered devices that will convert readily available vibrations into electrical power and no external source of energy will be required for operation, a three phase hybrid piezoelectric nanogenerator comprising of Lanthanum doped Lead Zirconate Titanate (PLZT), Polyvinyldene fluoride (PVDF) and Multi-walled Carbon Nanotubes (MWCNT) as supplement filler was fabricated. Piezoelectric composite films were prepared using tape casting technique, followed by hotpress. The addition of PLZT to PVDF and further MWCNT in PLZT-PVDF composite resulted in the enhancement of dielectric, ferroelectric, piezoelectric and energy storage properties. A maximum open circuit AC peak-to-peak voltage of 20 V was obtained from the nanogenerator after applying repeated human figure tapping and releasing motion on the sample. After rectification of the output AC voltage by bridge rectifier, the DC voltage was able to charge a 40 mu F commercial capacitor up to 8 V (2 mW power) and during discharging of the capacitor, around 50 LEDs were glowed. A 40 mu F capacitor was also charged by using the same method after applying foot pressure on the nanogenerator which delivered 1.5 mW power with 6 V DC voltage and 250 mu A short circuit current. Thus the amount of power delivered by the fabricated nanogenerator can drive several LEDs and charge capacitor which can be used for powering small electronic devices