Spin-phonon coupling and improved multiferroic properties of Zr substituted BiFeO3 nanoparticles

Zr substituted BiFeO₃ (BiFe_1?xZr_xO₃ with x = 0.03, 0.07, 0.10 and 0.15) nanoparticles were synthesized by sol–gel method. Powder X-ray diffraction studies showed rhombohedral crystal structure for x = 0.03–0.10 samples. The substitution induced structural transformation from rhombohedral to triclinic phase has been observed for x = 0.15. Raman analysis confirmed this structural transformation as also the distortion induced spin phonon coupling. Enhanced magnetic behaviour with saturation magnetization of 7.62 emu/g has been observed in x = 0.07 sample. The dielectric measurements indicated the strong magneto-electric coupling in the range of Neel temperature. The impedance study over a wider frequency and temperature range suggests decrease in conductivity in the samples with increasing Zr concentration. UV–Vis diffuse reflectance spectra shows the strong absorption of visible light suggesting the band gap values from 2.22 to 2.15 eV corresponding to x = 0.03–0.15 compositions.     

Comparative studies of pure BiFeO3 prepared by sol–gel versus conventional solid-state-reaction method

In this article, we studied the effect of synthesis route on the multifunctional properties of multiferroic BiFeO₃. BiFeO₃ powders were prepared by conventional solid-state-reaction and sol–gel route. X-ray diffraction (XRD) patterns for these samples were collected at different stages of synthesis to analyze the phase purity of the formation. The XRD patterns reveal that sample prepared by sol–gel route attains the low temperature phase formation as compared to the solid state route. Rietveld refinement has been performed for these samples and lattice parameters, cell volume bond length etc. have been calculated from XRD patterns. Phonon modes were studied by Fourier transform infrared spectroscopy measurements and bond length calculated from XRD shows the good agreement with the bond length calculated from IR spectra. UV–visible spectra showed that BFO nanoparticles exhibit absorption peak at wavelength ~521 nm and band gap is more for the sample prepared by sol–gel route than solid state. The room temperature (RT) magnetic hysteresis (M–H) curve shows the large value magnetization in the sample prepared by sol–gel route in comparison to the sample prepared by solid state route. Similar behaviour is seen in the P–E hysteresis curve. Room temperature dielectric properties of these samples revealed that there is dispersion in the low frequency range that shows normal dielectric characteristics.     

Respiratory Health of School Children in Relation to Their Body Mass Index (BMI) During Crop Residue Burning Events in North Western India

Particulate matter levels and physiological parameters of 150 school going children were monitored continually for 3 years (2013–2016) at three agriculturally active sites. Percent changes in physiological parameters like forced vital capacity, peak expiratory flow, etc. were estimated using mixed effect model with adjustment of covariates such as BMI. Results show that the increase in fine PM levels were much more in rice seasons than in wheat seasons. During the burning episodes, severe adverse effects on physiological parameters of the selected subjects were observed due to enhanced PM_2.5 levels. Significant changes were observed in FVC (? 5.27 to ? 7.53%) and PEF (? 4.89 to ? 7.12%) in comparison to FEV₁ and FEF_25–75%. Respiratory health in terms of FVC and PEF corresponded very well with the body mass indices of the human subjects for different PM levels in the ambient air. The subjects having lower BMI level were affected more than those with normal and high BMI on exposure to same level of fine particulate matter. It has been concluded that the trends of fall in respiratory parameters were alarming especially for the subjects with lower and higher BMI during crop residue burning episodes.     

Epidemiological Study on Respiratory Health of School Children of Rural Sites of Malwa Region (India) During Post-harvest Stubble Burning Events

A study on effects of particulate matter fractions (PM₁₀, PM_2.5 and PM₁) on health of school children was done from September 2014 to December 2015 covering one wheat and two rice crop seasons. The study was undertaken at 3 rural sites in the districts of Patiala, Fatehgarh Sahib and Sangrur (Malwa region of Punjab). The monthly average values of PM₁₀, PM_2.5 and PM₁ were about 3–4 times higher than the National Ambient Air Quality Standards (NAAQS) given by Central Pollution Control Board during the crop residue burning periods. The MODIS data images of crop residue burning events confirmed the active fire operations over the region. The lung function parameters (Forced Vital Capacity, Forced Expiratory Volume in one second) of children (10–16 years) decreased with increase in particulate matter concentration while no significant effect was observed on Oxygen saturation level of children. The decrease in Forced Vital Capacity was slightly more in male subjects as compared to the female population. The sharp decrease in Pulmonary Function Test parameters during the crop residue burning period indicated the severity of the episodic burning events on the health of the children.     

Sm doping effect on structural,morphological, luminescence and antibacterial activity of CdO nanoparticles

Undoped cadmium oxide along with samarium doped CdO are synthesized by simple soft precipitation method. Resulting precursor was calcined at 400 °C for 2 h. As a result of heating, a pure material was produced. The obtained compound possesses a cubic crystalline structure at nanoscale. Also, FESEM image showed that the resulting material is composed of nanoparticles and its size decreases with increase of Sm doping relative with the particle size calculated from XRD. The photoluminescence shows the emission of violet and blue colour peaks and the peak at 468 nm which is responsible for a better antibacterial activity. The synthesized nanopowders are subjected to two different gram positive (Staphylococcus aureus and Enterococcus faecalis) and two different gram negative (Escherichia coli and Klebsiella pneumoniae) bacterial strains respectively. It is noted that there are high activity of the Sm doped CdO towards gram negative bacteria.     

Energy‐Autonomous,Flexible, and Transparent Tactile Skin

Tactile or electronic skin is needed to provide critical haptic perception to robots and amputees, as well as in wearable electronics for health monitoring and wellness applications. Energy autonomy of skin is a critical feature that would enable better portability and longer operation times. This study shows a novel structure, consisting of a transparent tactile sensitive layer based on single‐layer graphene, and a photovoltaic cell underneath as a building block for energy‐autonomous, flexible, and tactile skin. Transparency of the touch sensitive layer is considered a key feature to allow the photovoltaic cell to effectively harvest light. Moreover, ultralow power consumed by the sensitive layer (20 nW cm^?2) further reduces the photovoltaic area required to drive the tactile skin. In addition to its energy autonomy, the fabricated skin is sensitive to touch, mainly because a transparent polymeric protective layer, spin‐coated on the sensor's active area, makes the coplanar capacitor sensitive to touch, detecting minimum pressures of 0.11 kPa with a uniform sensitivity of 4.3 Pa^?1 along a broad pressure range. Finally, the tactile skin patches are integrated on a prosthetic hand, and the responses of the sensors for static and dynamic stimuli are evaluated by performing tasks, ranging from simple touching to grabbing of soft objects.     

Design and Simulation of FBAR for Quality Factor Enhancement

Thin film bulk acoustic resonator (FBAR) higher quality factor (Q) provides steep skirt and low insertion losses in the pass band. In this paper, three different loss sources are identified and FBAR is design and simulated in order to reduce the losses. Firstly, the FBAR’s top electrode is simulated for the areas of 150 × 150, 300 × 300 and 400 × 400 μm² and the quality factor is improved as the area increased to 102, 432.6 and 743.7 respectively. The impedance of the FBAR is reduced as the area of the electrode is increased. Secondly, the anchor width is reduced from 60 to 45 μm and the quality factor is increased from 341 to 432.6 respectively. The losses through the anchor reduce as the anchor reduces. Electrode area and anchor area simulation are showing the notable effect and no other paper is reported for the comparison. Thirdly, the damping factor coefficient (β) is varied as 4.7e^?14, 3.84e^?14 and 2.5e^?14. The quality factor is increased as the damping factor reduces and reported as 283.2, 341.2 and 444.5 respectively. The damping reduction leads the FBAR structure to vibrate more freely at the resonance. The losses through damping are reduced and more energy has stored at the resonance so it increases the quality factor.     

Structural and microwave properties of Ag-doped strontium hexaferrite

A series of silver-doped strontium hexaferrite with the chemical formula SrAg_ZFe_12-zO₁₉ (0.0?≤?z?≤?1.0) were synthesized by the Co-precipitation method. The crystal structure, morphology, and properties of microwave absorption with Ag concentration were studied. The structural analysis by XRD revealed that the samples are crystallized with an M-type hexagonal structure. The values of lattice parameters, the volume of the unit cell, and X-ray density are increasing with the increase of Ag doping. The least values of Rietveld refinements have confirmed a good correlation between experimental and calculated data. Hexagonal plate-like morphology was observed in SEM images and the grain size decreases with Ag doping. Microwave properties have been measured by a vector network analyzer. Real and imaginary parts of electrical permittivity dependence with the frequencies in X-band (8–12 GHz) have been studied. The Reflection loss (RL) was investigated for all samples in X-band frequencies. Maximum RL of ? 21.95 dB at 10.0 GHz was observed for the composition of silver, z?=?0.4. Improved RL when compared with the pure sample indicating enhanced impedance matching and attenuation constant hence the material can show maximum energy loss for the incident microwaves. The results so obtained are explained based on composition and microwave phenomena. The present studies have confirmed the nature of microwave absorption for Ag-doped strontium hexaferrite.

     

Synthesis and modulation of the optical properties of carbon quantum dots using microwave radiation

Abstract

Carbon quantum dots have exhibited highly fluorescent characteristics as nanomaterials. Soluble in water and easily synthesized by multiple simple techniques, there are immense fabrication possibilities by permuting their properties via changing precursors, synthesis route, reaction parameters, etc. As economic and environment-friendly seed material, they are being viewed as an alternative to conventional fluorescent materials in myriad of applications including displays, cancer detection, drug delivery carriers in biomedicine, absorbing material in photovoltaics, etc. In this work, the hydrophilic carbon quantum dots were synthesized from the aqueous solution of citric acid and urea through microwave radiation for varying heat durations. The method is facile, faster and friendly to the environment without any need for high temperature and complicated chemical techniques. It was observed that the bandgap of the fabricated carbon quantum dots and its optical properties namely absorbance, photoluminescence enhanced with an increase in exposure of samples to heat up to an optimum limit, owing to the increase in density of states. However, further exposure to heat for longer duration degraded the absorbance and bandgap while photoluminescence gets saturated. Stokes’ shift revealed that all the synthesized carbon quantum dots possess stable emission. This was reconfirmed from consistent emission peak positions under varying excitation in the samples. The absorbance and PL spectrum exhibited by the synthesized dots makes it a suitable material for boosting the performance of organic solar cell.     

Synthesis and characterization of PZT: CF magnetoelectric composites

Here, we report the structural, dielectric, ferroelectric, piezoelectric and magnetic properties of ME composites of Lead Zirconate Titanate (PZT) and Cobalt ferrite (CF) with compositional formula (1?x) PbZr_0.55Ti_0.45O₃ + (x) CoFe₂O₄, (x = 0.00, 0.05, 0.10, 0.15 and 1.00 by weight). The samples were synthesized by conventional solid state reaction. The formation of perovskite tetragonal and spinel structure in the composites are confirmed by X-ray diffraction studies. Microstructural study of all samples was done by SEM analysis and average grain size was also calculated. The dielectric properties of samples were studied as a function of frequency and as a function of temperature (30°C – 500°C) respectively. P-E hysteresis loop at room temperature and piezoelectric coefficient were measured to study the ferroelectric and piezoelectric properties. To confirm the ferromagnetic behavior of the composites M-H hysteresis loop measurement was carried out. The Magnetoelectric voltage coefficient (dE/dH) was measured as a function of applied DC magnetic field. The maximum ME output of 389μV/ (cm.Oe) was observed for the composite with x = 0.15.